drm/vc4: Consolidate Hardware Revision Check

drm/vc4: Consolidate Hardware Revision Check

A new generation of controller has been introduced with the
BCM2711/RaspberryPi4. This generation needs a bunch of quirks, and over
time we've piled on a number of checks in most parts of the drivers.

All these checks are performed several times, and are not always
consistent. Let's create a single, global, variable to hold it and use
it everywhere.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>