aarch64: Rename AARCH64_ISA architecture-level macros

aarch64: Rename AARCH64_ISA architecture-level macros

All AARCH64_ISA_* architecture-level macros except AARCH64_ISA_V8_R
are for the A profile: they cause __ARM_ARCH_PROFILE to be set to
'A' and they are associated with architecture names like armv8.4-a.

It's convenient for later patches if we make this explicit
by adding an "A" to the name.  Also, rather than add an underscore
(as for V8_R) it's more convenient to add the profile directly
to the number, like we already do in the ARCH_IDENT field of the
aarch64-arches.def entries.

gcc/
	* config/aarch64/aarch64.h (AARCH64_ISA_V8_2, AARCH64_ISA_V8_3)
	(AARCH64_ISA_V8_4, AARCH64_ISA_V8_5, AARCH64_ISA_V8_6)
	(AARCH64_ISA_V9, AARCH64_ISA_V9_1, AARCH64_ISA_V9_2)
	(AARCH64_ISA_V9_3): Add "A" to the end of the name.
	(AARCH64_ISA_V8_R): Rename to AARCH64_ISA_V8R.
	(TARGET_ARMV8_3, TARGET_JSCVT, TARGET_FRINT, TARGET_MEMTAG): Update
	accordingly.
	* common/config/aarch64/aarch64-common.cc
	(aarch64_get_extension_string_for_isa_flags): Likewise.
	* config/aarch64/aarch64-c.cc
	(aarch64_define_unconditional_macros): Likewise.