drm/vc4: drv: Register a different driver on BCM2711

Prior to the BCM2711/RaspberryPi4, the GPU was a part of the display
components of the SoC. It was thus a part of the vc4 driver.

However, with the BCM2711, it got split out and thus the v3d driver was
created. The vc4 driver now only handles the display part.

We didn't properly split out the code when doing the BCM2711 support
though, and most of the code around buffer allocations is still
involved, even though it doesn't have the backing hardware anymore.

Let's start the split out by creating a new drm_driver that only reports
and uses what we support on the BCM2711. The ioctl were properly
filtered already, but we were still exposing a .gem_create_object hook,
as well as having an .open and .postclose hooks which are only relevant
on older generations.

Reviewed-by: Melissa Wen <mwen@igalia.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20220610115149.964394-6-maxime@cerno.tech