drm/edid: Add option to report basic audio support with a generic edid

Hardware that fails to read the edid is quite common.
The kernel provides a mechanism to use one a of a few
pre-built generic edid files for getting a basic video mode.

However there is no easy was to add basic audio support,
which requires a CTA extension block to report capabilities.

Add an module option to request this.

Signed-off-by: Dom Cobley <popcornmix@gmail.com>