It's incredibly difficult to diagnose early EFI boot issues without
special hardware because earlyprintk=vga doesn't work on EFI systems.
Add support for writing to the EFI framebuffer, via earlyprintk=efi,
which will actually give users a chance of providing debug output.
Cc: H. Peter Anvin <hpa@zytor.com> Acked-by: Ingo Molnar <mingo@kernel.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Jones <pjones@redhat.com> Signed-off-by: Matt Fleming <matt.fleming@intel.com>