RISC-V: Add basic Zaamo and Zalrsc support

RISC-V: Add basic Zaamo and Zalrsc support

There is a proposal to split the A extension into two parts: Zaamo and Zalrsc.
This patch adds basic support by making the A extension imply Zaamo and
Zalrsc.

Proposal: https://github.com/riscv/riscv-zaamo-zalrsc/tags

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc: Add Zaamo and Zalrsc.
	* config/riscv/arch-canonicalize: Make A imply Zaamo and Zalrsc.
	* config/riscv/riscv.opt: Add Zaamo and Zalrsc
	* config/riscv/sync.md: Convert TARGET_ATOMIC to TARGET_ZAAMO and
	TARGET_ZALRSC.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/attribute-15.c: Adjust expected arch string.
	* gcc.target/riscv/attribute-16.c: Ditto.
	* gcc.target/riscv/attribute-17.c: Ditto.
	* gcc.target/riscv/attribute-18.c: Ditto.
	* gcc.target/riscv/pr110696.c: Ditto.
	* gcc.target/riscv/rvv/base/pr114352-1.c: Ditto.
	* gcc.target/riscv/rvv/base/pr114352-3.c: Ditto.

Signed-off-by: Edwin Lu <ewlu@rivosinc.com>
Co-authored-by: Patrick O'Neill <patrick@rivosinc.com>