disas/riscv: enable disassembly for compressed sspush/sspopchk

disas/riscv: enable disassembly for compressed sspush/sspopchk

sspush and sspopchk have equivalent compressed encoding taken from zcmop.
cmop.1 is sspush x1 while cmop.5 is sspopchk x5. Due to unusual encoding
for both rs1 and rs2 from space bitfield, this required a new codec.

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241008225010.1861630-20-debug@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>