RISC-V: Add Zalrsc amo-op patterns

RISC-V: Add Zalrsc amo-op patterns

All amo<op> patterns can be represented with lrsc sequences.
Add these patterns as a fallback when Zaamo is not enabled.

gcc/ChangeLog:

	* config/riscv/sync.md (atomic_<atomic_optab><mode>): New expand pattern.
	(amo_atomic_<atomic_optab><mode>): Rename amo pattern.
	(atomic_fetch_<atomic_optab><mode>): New lrsc sequence pattern.
	(lrsc_atomic_<atomic_optab><mode>): New expand pattern.
	(amo_atomic_fetch_<atomic_optab><mode>): Rename amo pattern.
	(lrsc_atomic_fetch_<atomic_optab><mode>): New lrsc sequence pattern.
	(atomic_exchange<mode>): New expand pattern.
	(amo_atomic_exchange<mode>): Rename amo pattern.
	(lrsc_atomic_exchange<mode>): New lrsc sequence pattern.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/amo-zaamo-preferred-over-zalrsc.c: New test.
	* gcc.target/riscv/amo-zalrsc-amo-add-1.c: New test.
	* gcc.target/riscv/amo-zalrsc-amo-add-2.c: New test.
	* gcc.target/riscv/amo-zalrsc-amo-add-3.c: New test.
	* gcc.target/riscv/amo-zalrsc-amo-add-4.c: New test.
	* gcc.target/riscv/amo-zalrsc-amo-add-5.c: New test.

Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>