In the drm subsystem, the source physical address is, in most cases,
available without having to parse the EDID again. Add notes about
preferring to use the pre-parsed address instead.

Cc: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: linux-media@vger.kernel.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Link: https://patchwork.freedesktop.org/patch/msgid/20230831105144.25923-1-jani.nikula@intel.com