drm/i915: Shrink TV modes const data

Make struct video_levels and struct tv_mode use data types
of sufficient width to save approximately one kilobyte in
the .rodata section.

v2: Do not align struct members. (Jani Nikula, Joonas Lahtinen)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1476353366-13931-1-git-send-email-tvrtko.ursulin@linux.intel.com