boards/esp32s3-lhcbit: switch defconfigs to nxinit entrypoint

Switch the esp32s3-lhcbit usbnsh defconfig from nsh_main to nxinit
(init_main) as the system init entry point, matching the
lckfb-szpi-esp32s3 board's existing nxinit configs (see 73c949c87e)
for consistency across esp32s3 boards.

- CONFIG_INIT_ENTRYPOINT switched to "init_main"
- CONFIG_INIT_STACKSIZE set to 8192. Measured on lckfb-szpi-esp32s3
  with CONFIG_STACK_COLORATION=y on the worst case available: a config
  whose init.rc starts two services (console sh + adbd). At the 2048
  Kconfig default the board panics at runtime (xtensa_user_panic, task
  "sh"); at 4096 init_main reaches FILLED=99.5%, i.e. no headroom; at
  8192 it settles at USED=4336 (53.6%). A single-service config only
  fills 46.9% of a 3072-byte init stack, so 8192 is deliberately
  uniform rather than minimal: it covers the two-service worst case
  with roughly 2x margin and keeps every defconfig off the 2048
  default, where the init stack overflows and clobbers the global
  inode/mount tree - the procfs mount disappears, "ls /" crashes in
  read_pseudodir and "ps" reports "/proc not mounted".
- CONFIG_SYSTEM_NXINIT=y added, plus its direct Kconfig dependencies
  (CONFIG_EXPERIMENTAL, CONFIG_LIBC_EXECFUNCS, CONFIG_SCHED_CHILD_STATUS,
  which depends on CONFIG_SCHED_HAVE_PARENT)
- CONFIG_SYSTEM_NSH_STACKSIZE=8192 added: nsh now runs as a service
  spawned by init.rc instead of being init itself, so the shell
  workload is carried by its own stack rather than the init stack.
  Without this it falls back to CONFIG_DEFAULT_TASK_STACKSIZE (2048
  unless the defconfig overrides it) and crashes in getumask while
  running "ps", too small to reach the procfs read path.
- ETC_ROMFS/FS_ROMFS added, needed to ship init.rc via the board's
  ROMFS

nsh continues to run as a console service started by init.rc
(boards/xtensa/esp32s3/common/src/etc/init.d/init.rc), not as the
top-level init.

Verified the usbnsh defconfig builds cleanly with make. Runtime
behavior (init_main spawning nsh as a console service) was confirmed
on lckfb-szpi-esp32s3 hardware, which shares the same nxinit/init.rc
mechanism; this board has no hardware attached for a flash/boot pass
in this session, so the build-verified defconfig is the extent of
local testing here.

Assisted-by: Kiro:claude-sonnet-5
Assisted-by: Kiro:claude-opus-5
Signed-off-by: wangjianyu3 <wangjianyu3@xiaomi.com>

boards/xtensa/esp32s3/esp32s3-lhcbit/configs/usbnsh/defconfig

@@ -30,13 +30,17 @@ CONFIG_DEBUG_FULLOPT=y
 CONFIG_DEBUG_SYMBOLS=y
 CONFIG_ESP32S3_OTG=y
 CONFIG_ESP32S3_UART0=y
+CONFIG_ETC_ROMFS=y
+CONFIG_EXPERIMENTAL=y
 CONFIG_FS_PROCFS=y
+CONFIG_FS_ROMFS=y
 CONFIG_HAVE_CXX=y
 CONFIG_HAVE_CXXINITIALIZE=y
 CONFIG_IDLETHREAD_STACKSIZE=3072
-CONFIG_INIT_ENTRYPOINT="nsh_main"
-CONFIG_INIT_STACKSIZE=4096
+CONFIG_INIT_ENTRYPOINT="init_main"
+CONFIG_INIT_STACKSIZE=8192
 CONFIG_INTELHEX_BINARY=y
+CONFIG_LIBC_EXECFUNCS=y
 CONFIG_LINE_MAX=64
 CONFIG_NSH_BUILTIN_APPS=y
 CONFIG_NSH_FILEIOSIZE=512
@@ -45,9 +49,13 @@ CONFIG_PREALLOC_TIMERS=4
 CONFIG_RAM_SIZE=114688
 CONFIG_RAM_START=0x20000000
 CONFIG_RR_INTERVAL=200
+CONFIG_SCHED_CHILD_STATUS=y
+CONFIG_SCHED_HAVE_PARENT=y
 CONFIG_SCHED_WAITPID=y
 CONFIG_START_DAY=6
 CONFIG_START_MONTH=12
 CONFIG_START_YEAR=2011
 CONFIG_SYSLOG_BUFFER=y
 CONFIG_SYSTEM_NSH=y
+CONFIG_SYSTEM_NSH_STACKSIZE=8192
+CONFIG_SYSTEM_NXINIT=y