Add expander for movp2hi and movp2qi.

Add expander for movp2hi and movp2qi.

2020-08-30  Uros Bizjak    <ubizjak@gmail.com>

gcc/ChangeLog:
	PR target/96744
	* config/i386/i386-expand.c (split_double_mode): Also handle
	E_P2HImode and E_P2QImode.
	* config/i386/sse.md (MASK_DWI): New define_mode_iterator.
	(mov<mode>): New expander for P2HI,P2QI.
	(*mov<mode>_internal): New define_insn_and_split to split
	movement of P2QI/P2HI to 2 movqi/movhi patterns after reload.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/double_mask_reg-1.c: New test.