edid: add edid_get_timing_validate() variant to filter out edid modes

The original edid_get_timing() function returns the first valid timing,
but on some plaforms, we could only supports a subset of the listed
monitot's navite timing.

Let's introduce a edid_get_timing_validate() adding a mode_valid callback
including a private cookie pointer.

If the callback returns false, the current timing is discared and the next
one is checked. If no valid & supported timings are found, the function
would return an error.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>