RISC-V: KVM: selftests: Add get-reg-list test for STA registers

Add SBI STA and its two registers to the get-reg-list test.

Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Anup Patel <anup@brainfault.org>