MIPS: jazz: always allow little-endian builds

The kernel test robot keeps reporting the same bug when it
shows up in new files after random unrelated patches:

In file included from arch/mips/include/uapi/asm/byteorder.h:13,
                 from arch/mips/include/asm/bitops.h:20,
                 from include/linux/bitops.h:26,
                 from include/linux/kernel.h:12,
                 from include/linux/clk.h:13,
                 from drivers/base/regmap/regmap-mmio.c:7:
include/linux/byteorder/big_endian.h:8:2: warning: #warning inconsistent configuration, needs CONFIG_CPU_BIG_ENDIAN [-Wcpp]
    8 | #warning inconsistent configuration, needs CONFIG_CPU_BIG_ENDIAN
      |  ^~~~~~~
drivers/base/regmap/regmap-mmio.c: In function 'regmap_mmio_gen_context':
>> drivers/base/regmap/regmap-mmio.c:274:2: error: duplicate case value
  274 |  case REGMAP_ENDIAN_NATIVE:
      |  ^~~~
drivers/base/regmap/regmap-mmio.c:246:2: note: previously used here
  246 |  case REGMAP_ENDIAN_NATIVE:

The problem is that some randconfig builds end up on the MIPS jazz
platform with neither CONFIG_CPU_BIG_ENDIAN nor CONFIG_CPU_LITTLE_ENDIAN
because no specific machine is selected. As it turns out, all jazz
machines support little-endian kernels, so this can simply be allowed
globally.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>