KVM: arm64: selftests: Move finalize_vcpu back to run_test

No functional changes. Just move the finalize_vcpu call back to
run_test and do weak function trick to prepare for the opration
in riscv.

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