Remove implicit default credentials and add build-time validation.
Add check_passwd_keys.sh and gen_passwd_keys.sh; run key setup via
passwd_keys.mk before config.h is generated. Mirror the same logic in
cmake/nuttx_add_romfs.cmake for CMake builds.
BREAKING CHANGE: Builds with CONFIG_BOARD_ETC_ROMFS_PASSWD_ENABLE=y now
require an explicit admin password and non-default TEA keys. The
Kconfig default password "Administrator" and default TEA keys are no
longer accepted. Fix: run make menuconfig, set Admin password under
Board Selection -> Auto-generate /etc/passwd, enable random TEA keys or
set CONFIG_FSUTILS_PASSWD_KEY1..4 manually, and use NSH login with
Encrypted password file verification.
Signed-off-by: Abhishek Mishra <mishra.abhishek2808@gmail.com>
