Platform: x86: chromeos_laptop - add i915 gmbuses to adapter names

Add the two other i2c buses (vga and panel) from i915.
Chromebook Pixel has input and light sensor devices on these busses.

Signed-off-by: Benson Leung <bleung@chromium.org>
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>