AArch64: Block combine_and_move from creating FP literal loads

AArch64: Block combine_and_move from creating FP literal loads

The IRA combine_and_move pass runs if the scheduler is disabled and aggressively
combines moves.  The movsf/df patterns allow all FP immediates since they rely
on a split pattern.  However splits do not happen during IRA, so the result is
extra literal loads.  To avoid this, split early during expand and block
creation of FP immediates that need this split.  Mark a few testcases that
rely on late splitting as xfail.

double f(void) { return 128.0; }

-O2 -fno-schedule-insns gives:

	adrp	x0, .LC0
	ldr	d0, [x0, #:lo12:.LC0]
	ret

After patch:

	mov	x0, 4638707616191610880
	fmov	d0, x0
	ret

Passes bootstrap & regress, OK for commit?

gcc:
	* config/aarch64/aarch64.md (movhf_aarch64): Use aarch64_valid_fp_move.
	(movsf_aarch64): Likewise.
	(movdf_aarch64): Likewise.
	* config/aarch64/aarch64.cc (aarch64_valid_fp_move): New function.
	* config/aarch64/aarch64-protos.h (aarch64_valid_fp_move): Likewise.

gcc/testsuite:
	* gcc.target/aarch64/dbl_mov_immediate_1.c: Add xfail for -0.0.
	* gcc.target/aarch64/fmul_scvtf_1.c: Fixup test cases, add xfail,
	reduce duplication.