i386: Use various predicates instead of open coding them

i386: Use various predicates instead of open coding them

No functional changes.

gcc/ChangeLog:

	* config/i386/i386-expand.cc (ix86_expand_move):
	Use MEM_P predicate instead of open coding it.
	(ix86_erase_embedded_rounding):
	Use NONJUMP_INSN_P predicate instead of open coding it.
	* config/i386/i386-features.cc (convertible_comparison_p):
	Use REG_P predicate instead of open coding it.
	* config/i386/i386.cc (ix86_rtx_costs):
	Use SUBREG_P predicate instead of open coding it.