package/cog: support choosing either DRM or FDO platform

package/cog: support choosing either DRM or FDO platform

A new DRM platform has landed, now you can choose to build with the
DRM or FDO platform, or neither. If neither are selected, Cog will
fallback to a simple WPE backend like WPEBackend-rdk
(https://github.com/WebPlatformForEmbedded/WPEBackend-rdk).

Don't be confused that in both cases the *wpebackend-fdo* package is
required. This is an unfortunate naming issue.

Signed-off-by: Charlie Turner <cturner@igalia.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>