gbm: manage only the required set of DRI extensions

gbm: manage only the required set of DRI extensions

Currently GBM attempts to know all the extensions that might be required
by EGL/DRM [at some later stage].

That is a bit unclear and we often forget to update GBM as EGL gets
attention.

To avoid that, simply let EGL manage it's own required extensions based
on the base primitive (screen) we provide it.

v2: Rework the approach - GBM should not dive into EGL/DRM.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Tested-by: Rob Herring <robh@kernel.org>