KVM: arm64: selftests: Remove print_reg's dependency on vcpu_config

print_reg() and its helpers only use the vcpu_config pointer for
config_name(). So just pass the config name in instead, which is used
as a prefix in asserts. print_reg() can now be compiled independently
of config_name().

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