nb/intel/*/graphic_init: use sizeof instead of hardcoding edid size

Change-Id: I2b8c4ef75cca9f9d5251789cda4187a02076b69d
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/16964
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Martin Roth <martinroth@google.com>
6 files changed