LoongArch: Add ARCH_HAS_SET_MEMORY support

Add set_memory_ro/rw/x/nx architecture hooks to change the page
attribution.

Use own set_memory.h rather than generic set_memory.h (i.e.
include/asm-generic/set_memory.h), because we want to add other function
prototypes here.

Note: We can only set attributes for KVRANGE/XKVRANGE kernel addresses.

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>