i386: Allow SI, DI and TImode pushes from XMM registers

i386: Allow SI, DI and TImode pushes from XMM registers

Also change XMM register constraint from "x" to "v" in FP push insns.

gcc/ChangeLog:

2020-05-15  Uroš Bizjak  <ubizjak@gmail.com>

	* config/i386/i386.md (SWI48DWI): New mode iterator.
	(*push<mode>2): Allow XMM registers.
	(*pushdi2_rex64): Ditto.
	(*pushsi2_rex64): Ditto.
	(*pushsi2): Ditto.
	(push XMM reg splitter): New splitter

	(*pushdf) Change "x" operand constraint to "v".
	(*pushsf_rex64): Ditto.
	(*pushsf): Ditto.