RISC-V: Add support for Zabha extension

RISC-V: Add support for Zabha extension

The Zabha extension adds support for subword Zaamo ops.

Extension: https://github.com/riscv/riscv-zabha.git
Ratification: https://jira.riscv.org/browse/RVS-1685

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc
	(riscv_subset_list::to_string): Skip zabha when not supported by
	the assembler.
	* config.in: Regenerate.
	* config/riscv/arch-canonicalize: Make zabha imply zaamo.
	* config/riscv/iterators.md (amobh): Add iterator for amo
	byte/halfword.
	* config/riscv/riscv.opt: Add zabha.
	* config/riscv/sync.md (atomic_<atomic_optab><mode>): Add
	subword atomic op pattern.
	(zabha_atomic_fetch_<atomic_optab><mode>): Add subword
	atomic_fetch op pattern.
	(lrsc_atomic_fetch_<atomic_optab><mode>): Prefer zabha over lrsc
	for subword atomic ops.
	(zabha_atomic_exchange<mode>): Add subword atomic exchange
	pattern.
	(lrsc_atomic_exchange<mode>): Prefer zabha over lrsc for subword
	atomic exchange ops.
	* configure: Regenerate.
	* configure.ac: Add zabha assembler check.
	* doc/sourcebuild.texi: Add zabha documentation.

gcc/testsuite/ChangeLog:

	* lib/target-supports.exp: Add zabha testsuite infra support.
	* gcc.target/riscv/amo/inline-atomics-1.c: Remove zabha to continue to
	test the lr/sc subword patterns.
	* gcc.target/riscv/amo/inline-atomics-2.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-subword-amo-add-char-acq-rel.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-subword-amo-add-char-acquire.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-subword-amo-add-char-relaxed.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-subword-amo-add-char-release.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-rvwmo-subword-amo-add-char-seq-cst.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-subword-amo-add-char-acq-rel.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-subword-amo-add-char-acquire.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-subword-amo-add-char-relaxed.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-subword-amo-add-char-release.c: Ditto.
	* gcc.target/riscv/amo/zalrsc-ztso-subword-amo-add-char-seq-cst.c: Ditto.
	* gcc.target/riscv/amo/zabha-all-amo-ops-char-run.c: New test.
	* gcc.target/riscv/amo/zabha-all-amo-ops-short-run.c: New test.
	* gcc.target/riscv/amo/zabha-rvwmo-all-amo-ops-char.c: New test.
	* gcc.target/riscv/amo/zabha-rvwmo-all-amo-ops-short.c: New test.
	* gcc.target/riscv/amo/zabha-rvwmo-amo-add-char.c: New test.
	* gcc.target/riscv/amo/zabha-rvwmo-amo-add-short.c: New test.
	* gcc.target/riscv/amo/zabha-ztso-amo-add-char.c: New test.
	* gcc.target/riscv/amo/zabha-ztso-amo-add-short.c: New test.

Co-Authored-By: Patrick O'Neill <patrick@rivosinc.com>
Signed-Off-By: Gianluca Guida <gianluca@rivosinc.com>
Tested-by: Andrea Parri <andrea@rivosinc.com>