ARM MALI GPU

I have been working on trying to port the Linux panfrost DRM driver to
NetBSD.

Have run out of ideas on how to configure the MMU on the GPU, I can't
see any differences to what Linux is doing.

Adding extra debug code does change the behaviour a bit so maybe I need
more cache flush or memory barrier instructions.

Linux only seems to setup memory pages as inner shared in the CPU page
table same as NetBSD.

My latest version of the file with the MMU setup code is at:

<https://ftp.netbsd.org/pub/NetBSD/misc/rjs/drm/linux_device.c.gz>