target/riscv: Check 'A' and split extensions for atomic instructions

target/riscv: Check 'A' and split extensions for atomic instructions

Following the pattern for 'M' and Zmmul check if either the 'A'
extension is enabled or the appropriate split extension for the
instruction.

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20240123111030.15074-3-rbradford@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>