MAINTAINERS: RISC-V: KVM: Add another kselftests path

With the introduction of the get-reg-list test for riscv, another
directory has been added that should be tracked by riscv kvm
maintainers.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Haibo Xu <haibo1.xu@intel.com>
Signed-off-by: Anup Patel <anup@brainfault.org>