[AArch64] Prefer FPRs over GPRs for INSR

[AArch64] Prefer FPRs over GPRs for INSR

INSR of GPRs involves a cross-file move while INSR of FPRs doesn't.
We should therefore disparage the GPR version relative to the FPR
version.

The patch also adds MOVPRFX handling, but this is only tested
properly by the ACLE.

2019-08-07  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/aarch64-sve.md (vec_shl_insert_<mode>): Add
	MOVPRFX alternatives.  Make the GPR alternatives more expensive
	than the FPR ones.

gcc/testsuite/
	* gcc.target/aarch64/sve/init_12.c: Expect w1 to be moved into
	a temporary FPR.

From-SVN: r274192