LoongArch: Try VMA lock-based page fault handling first

Attempt VMA lock-based page fault handling first, and fall back to the
existing mmap_lock-based handling if that fails.

The "ebizzy -mTRp" test on Loongson-3A6000 shows that PER_VMA_LOCK can
improve the benchmark by about 17.9% (97837.7 to 115430.8).

This is the LoongArch variant of "x86/mm: try VMA lock-based page fault
handling first".

Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>