x86/efi: Clear EFI_RUNTIME_SERVICES if failing to enter virtual mode

If enter virtual mode failed due to some reason other than the efi call
the EFI_RUNTIME_SERVICES bit in efi.flags should be cleared thus users
of efi runtime services can check the bit and handle the case instead of
assume efi runtime is ok.

Per Matt, if efi call SetVirtualAddressMap fails we will be not sure
it's safe to make any assumptions about the state of the system. So
kernel panics instead of clears EFI_RUNTIME_SERVICES bit.

Signed-off-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>