drm: Add 1600x1200 (UXGA) screen resolution to the built-in EDIDs

The 1600x1200 (UXGA) screen resolution was lacking in the set of
built-in selectable EDID screen resolutions that can be used to
repair misbehaving monitor firmware.

This patch adds the related data set and expands the documentation.

Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Acked-by: Paul Menzel <paulepanter@users.sourceforge.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>