Enable direct movement between gpr and mask registers in pass_reload.

Enable direct movement between gpr and mask registers in pass_reload.

Changelog
gcc/
	* config/i386/i386.c (inline_secondary_memory_needed):
	No memory is needed between mask regs and gpr.
	(ix86_hard_regno_mode_ok): Add condition TARGET_AVX512F for
	mask regno.
	* config/i386/i386.h (enum reg_class): Add INT_MASK_REGS.
	(REG_CLASS_NAMES): Ditto.
	(REG_CLASS_CONTENTS): Ditto.
	* config/i386/i386.md: Exclude mask register in
	define_peephole2 which is avaiable only for gpr.

gcc/testsuite/
	* gcc.target/i386/spill_to_mask-1.c: New tests.
	* gcc.target/i386/spill_to_mask-2.c: New tests.
	* gcc.target/i386/spill_to_mask-3.c: New tests.
	* gcc.target/i386/spill_to_mask-4.c: New tests.