Add the ability to choose a video mode using a command-line argument of
the form
	video=efifb:<xres>x<yres>
Signed-off-by: NArvind Sankar <nivedita@alum.mit.edu>
Link: https://lore.kernel.org/r/20200320020028.1936003-13-nivedita@alum.mit.eduSigned-off-by: NArd Biesheuvel <ardb@kernel.org>