kernel: disable CONFIG_CPU_LITTLE_ENDIAN in generic config

kernel: disable CONFIG_CPU_LITTLE_ENDIAN in generic config

Endianness depends on CPU architecture. CONFIG_CPU_(BIG/LITTLE)_ENDIAN should
be enabled on target or subtarget based on SoC architecture.

Fixes warning:
$ make kernel_oldconfig CONFIG_TARGET=subtarget
...
.config:1008:warning: override: CPU_LITTLE_ENDIAN changes choice state
....

Summary:
- ARC - only the CONFIG_CPU_BIG_ENDIAN symbol is defined for this architeture.
  If it is disabled then the processor operates in LITTLE_ENDIAN mode (default),
- ARM32 - CONFIG_CPU_LITTLE_ENDIAN symbol available since kernel 5.19. This
  option should be enabled after OpenWRT moves to kernel 6.x. After refreshing
  the kernel, the symbol disappears,
- ARM64 - enabled CONFIG_CPU_LITTLE_ENDIAN,
- MIPS - enabled relevant symbols,
- POWERPC -  enabled CONFIG_CPU_BIG_ENDIAN,
- UML - Symbols are not defined for this architecture,
- X86 - always little endian. Symbols are not defined for this architecture.

Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>