[AArch64] Handle scalars in cmp and shift immediate queries

[AArch64] Handle scalars in cmp and shift immediate queries

The SVE ACLE has convenience functions that take scalar arguments
instead of vectors.  This patch makes it easier to implement the shift
and compare functions by making the associated immediate queries work
for scalar immediates as well as vector duplicates of them.

The "const" codes in the predicates were a holdover from an early
version of the SVE port in which we used (const ...) wrappers for
variable-length vector constants.  I'll remove other instances
of them in a separate patch.

2019-10-29  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* config/aarch64/aarch64.c (aarch64_sve_cmp_immediate_p)
	(aarch64_simd_shift_imm_p): Accept scalars as well as vectors.
	* config/aarch64/predicates.md (aarch64_sve_cmp_vsc_immediate)
	(aarch64_sve_cmp_vsd_immediate): Accept "const_int", but don't
	accept "const".

From-SVN: r277556