KVM: riscv: selftests: Add Smnpm and Ssnpm to get-reg-list test

Add testing for the pointer masking extensions exposed to KVM guests.

Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Link: https://lore.kernel.org/r/20241016202814.4061541-11-samuel.holland@sifive.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>