boards/rp2040: switch waveshare nsh/usbnsh configs to nxinit entrypoint

[JianyuWang0623]

Summary

Switch CONFIG_INIT_ENTRYPOINT from nsh_main to nxinit's init_main for
the shell-capable configs of both waveshare-rp2040-zero and
waveshare-rp2040-lcd-1.28: nsh (UART console) and usbnsh (USB CDC/ACM
console). nsh now runs as a "console sh" service started by init.rc
instead of being the top-level init task, matching the pattern already used
on rv-virt/esp32s3/qemu.

• boards/arm/rp2040/common/src/Make.defs: add init.rc to RCSRCS,
  gated on CONFIG_ETC_ROMFS && CONFIG_SYSTEM_NXINIT, following the same
  pattern boards/risc-v/qemu-rv/rv-virt uses. Both waveshare boards share
  CONFIG_ARCH_BOARD_COMMON's common/src, so one copy of init.rc
  covers both boards.
• boards/arm/rp2040/common/src/etc/init.d/init.rc: new. Starts an nsh
  "console" service (restart_period 1000) on the "init" event. sh
  resolves directly through the existing builtin binfmt loader
  (apps/system/nsh's PROGNAME already registers both nsh and sh),
  so no CONFIG_LIBC_ENVPATH/CONFIG_FS_BINFS changes are needed here
  (these boards don't set CONFIG_LIBC_ENVPATH).
• boards/arm/rp2040/common/.gitignore: new, ignoring the etctmp/
  etctmp.c build byproducts that boards/Board.mk generates from
  init.rc under BOARD_COMMON_DIR, matching the existing
  boards/risc-v/qemu-rv/rv-virt/src/.gitignore precedent.
• 4 defconfigs (waveshare-rp2040-zero and waveshare-rp2040-lcd-1.28,
  each nsh + usbnsh): CONFIG_INIT_ENTRYPOINT="init_main",
  CONFIG_SYSTEM_NXINIT=y plus its previously-unset Kconfig deps
  (CONFIG_EXPERIMENTAL, CONFIG_LIBC_EXECFUNCS, CONFIG_SCHED_HAVE_PARENT,
  CONFIG_SCHED_CHILD_STATUS), and CONFIG_ETC_ROMFS=y /
  CONFIG_FS_ROMFS=y to ship init.rc via the standard /etc ROMFS
  auto-mount (sched/init/nx_bringup.c's nx_romfsetc()). Each defconfig
  regenerated with kconfig-tweak + make savedefconfig; verified
  byte-for-byte reproducible by re-running make savedefconfig from the
  committed file.

Impact

Image size impact (waveshare-rp2040-lcd-1.28:nsh, same toolchain):
nsh_main baseline text/data/bss = 159464/900/10748 (171112 total);
nxinit build = 174740/904/8204 (183848 total). RAM_SIZE is 270336
(264 KiB SRAM), comfortably clear of both.

CMake build support for RP2040's ETC_ROMFS is a known pre-existing gap
(see boards/arm/rp23xx/*/src/CMakeLists.txt's # TODO); left untouched
here to match that established precedent.

Testing Build Host

$ ./tools/checkpatch.sh -c -u -m -g origin/master..HEAD
Used config files:
    1: .codespellrc
✔️ All checks pass.

All 4 configs built cleanly with
make PICO_SDK_PATH=<pico-sdk> (arm-none-eabi-gcc 10.3.1):

board	config	text/data/bss
waveshare-rp2040-lcd-1.28	nsh	174740/904/8204
waveshare-rp2040-lcd-1.28	usbnsh	180680/752/11272
waveshare-rp2040-zero	nsh	174672/904/8272
waveshare-rp2040-zero	usbnsh	180552/752/11400

waveshare-rp2040-zero has no physical unit available to this contributor
(build-only verification for that board).

Hardware bring-up on waveshare-rp2040-lcd-1.28 (serial console, USB
CDC/ACM console, init.rc/ROMFS boot log, interactive shell) is still
pending — the only physical unit is currently in concurrent use by a
parallel workstream on the same fork. This PR is opened as draft and
will be updated with real UART/USB console boot logs and shell output
before being marked ready for review.

Related

Part of the RP2040 waveshare fastboot + nxinit + dual-partition bootloader
initiative (Stage 3 of 4).

[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb

[acassis]

Strange, github is failing: I will restart that job:

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Error: Unhandled error: HttpError
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