i386: Cleanup ix86_expand_{unary|binary}_operator issues

Move ix86_expand_unary_operator from i386.cc to i386-expand.cc, re-arrange
prototypes and do some cosmetic changes with the usage of TARGET_APX_NDD.

No functional changes.

gcc/ChangeLog:

	* config/i386/i386.cc (ix86_unary_operator_ok): Move from here...
	* config/i386/i386-expand.cc (ix86_unary_operator_ok): ... to here.
	* config/i386/i386-protos.h: Re-arrange ix86_{unary|binary}_operator_ok
	and ix86_expand_{unary|binary}_operator prototypes.
	* config/i386/i386.md: Cosmetic changes with the usage of
	TARGET_APX_NDD in ix86_expand_{unary|binary}_operator
	and ix86_{unary|binary}_operator_ok function calls.