x86/efi: Add EFI framebuffer earlyprintk support

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>

diff --cc Documentation/kernel-parameters.txt
Simple merge

diff --cc arch/x86/Kconfig.debug
Simple merge

diff --cc arch/x86/include/asm/efi.h
Simple merge

diff --cc arch/x86/kernel/early_printk.c
Simple merge

diff --cc arch/x86/platform/efi/Makefile
Simple merge

diff --cc arch/x86/platform/efi/early_printk.c
Simple merge