Refine maskstore patterns with UNSPEC_MASKMOV.

Refine maskstore patterns with UNSPEC_MASKMOV.

Similar like r14-2070-gc79476da46728e

If mem_addr points to a memory region with less than whole vector size
bytes of accessible memory and k is a mask that would prevent reading
the inaccessible bytes from mem_addr, add UNSPEC_MASKMOV to prevent
it to be transformed to any other whole memory access instructions.

gcc/ChangeLog:

	PR rtl-optimization/110237
	* config/i386/sse.md (<avx512>_store<mode>_mask): Refine with
	UNSPEC_MASKMOV.
	(maskstore<mode><avx512fmaskmodelower): Ditto.
	(*<avx512>_store<mode>_mask): New define_insn, it's renamed
	from original <avx512>_store<mode>_mask.