[AARCH64] use "arch_enabled" attribute for aarch64.

[AARCH64] use "arch_enabled" attribute for aarch64.

arm.md has some attributes "arch" and "arch_enabled" to aid enabling
and disabling insn alternatives based on the architecture being
targeted.  This patch introduces a similar attribute in the aarch64
backend.  The new attribute will be used to enable a new alternative
for the atomic_store insn in a future patch, but is an atomic change
in itself.

The new attribute has values "any", "fp", "fp16", "simd", and "sve".
These attribute values have been taken from the pre-existing
attributes "fp", "fp16", "simd", and "sve".

The standalone "fp" attribute has been reintroduced in terms of the
"arch" attribute as it's needed for the xgene1.md scheduling file --
the use in this file can't be changed to check for `(eq_attr "arch"
"fp")` as the file is reused by the arm.md machine description whose
'arch' attribute doesn't have an 'fp' value.

2018-08-23  Matthew Malcomson  <matthew.malcomson@arm.com>

	* config/aarch64/aarch64.md (arches): New enum.
	(arch): New enum attr.
	(arch_enabled): New attr.
	(enabled): Now uses arch_enabled only.
	(simd, sve, fp16): Removed attribute.
	(fp): Attr now defined in terms of 'arch'.
	(*mov<mode>_aarch64, *movsi_aarch64, *movdi_aarch64, *movti_aarch64,
	*movhf_aarch64, <optab><fcvt_target><GPF:mode>2,
	<FCVT_F2FIXED:fcvt_fixed_insn><GPF:mode>3,
	<FCVT_FIXED2F:fcvt_fixed_insn><GPI:mode>3): Merge 'fp' and 'simd'
	attributes into 'arch'.
	(*movsf_aarch64, *movdf_aarch64, *movtf_aarch64, *add<mode>3_aarch64,
	subdi3, neg<mode>2, <optab><mode>3, one_cmpl<mode>2,
	*<NLOGICAL:optab>_one_cmpl<mode>3, *xor_one_cmpl<mode>3,
	*aarch64_ashl_sisd_or_int_<mode>3, *aarch64_lshr_sisd_or_int_<mode>3,
	*aarch64_ashr_sisd_or_int_<mode>3, *aarch64_sisd_ushl): Convert use of
	'simd' attribute into 'arch'.
	(load_pair_sw_<SX:mode><SX2:mode>, load_pair_dw_<DX:mode><DX2:mode>,
	store_pair_sw_<SX:mode><SX2:mode>, store_pair_dw_<DX:mode><DX2:mode>):
	Convert use of 'fp' attribute to 'arch'.
	* config/aarch64/aarch64-simd.md (move_lo_quad_internal_<mode>,
	move_lo_quad_internal_<mode>): (different modes) Merge 'fp' and 'simd'
	into 'arch'.
	(move_lo_quad_internal_be_<mode>, move_lo_quad_internal_be_<mode>):
	(different modes) Merge 'fp' and 'simd' into 'arch'.
	(*aarch64_combinez<mode>, *aarch64_combinez_be<mode>): Merge 'fp' and
	'simd' into 'arch'.

From-SVN: r263811