[AArch64] Use simd_immediate_info for SVE predicate constants

[AArch64] Use simd_immediate_info for SVE predicate constants

This patch makes predicate constants use the normal simd_immediate_info
machinery, rather than treating PFALSE and PTRUE as special cases.
This makes it easier to add other types of predicate constant later.

2019-08-13  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/aarch64-protos.h (aarch64_output_ptrue): Delete.
	* config/aarch64/aarch64-sve.md (*aarch64_sve_mov<PRED_ALL:mode>):
	Use a single Dn alternative instead of separate Dz and Dm
	alternatives.  Use aarch64_output_sve_move_immediate.
	* config/aarch64/aarch64.c (aarch64_sve_element_int_mode): New
	function.
	(aarch64_simd_valid_immediate): Fill in the simd_immediate_info
	for predicates too.
	(aarch64_output_sve_mov_immediate): Handle predicate modes.
	(aarch64_output_ptrue): Delete.

From-SVN: r274372