x86/efi: Fix reboot_mode when EFI runtime services are disabled

When EFI runtime services are disabled, for example by the "noefi"
kernel cmdline parameter, the reboot_type could still be set to
BOOT_EFI causing reboot to fail.

Fix this by checking if EFI runtime services are enabled.

Signed-off-by: Stefan Assmann <sassmann@kpanic.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170724122248.24006-1-sassmann@kpanic.de


[ Fixed 'not disabled' double negation. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>