LoongArch: Adjust arch/loongarch/Kconfig

mainline inclusion
from mainline-v6.0-rc1
commit f30d1f49
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5OHOB


CVE: NA

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1, ACPI, EFI and SMP are mandatories for LoongArch, select them
unconditionally to avoid various build errors for 'make randconfig'.
2, Move the MMU_GATHER_MERGE_VMAS selection to the correct place.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>