amend! drm/panthor: Allow driver compilation

drm/panthor: Allow driver compilation

Now that all blocks are available, we can add/update Kconfig/Makefile
files to allow compilation.

v3:
- Fix dependencies in Kconfig
- Expand help text to (hopefully) describe which GPUs are to be
  supported by this driver and which are for panfrost.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Steven Price <steven.price@arm.com>