KVM: riscv: selftests: Add Zacas extension to get-reg-list test

The KVM RISC-V allows Zacas extension for Guest/VM so add this
extension to get-reg-list test.

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