disas/riscv: enable `lpad` disassembly

disas/riscv: enable `lpad` disassembly

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Co-developed-by: Jim Shu <jim.shu@sifive.com>
Co-developed-by: Andy Chiu <andy.chiu@sifive.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241008225010.1861630-9-debug@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>