drm/nv40/gr: rewrite/split context takedown functions
drm/nv40/gr: rewrite/split context takedown functions

It's completely pointless to save the PGRAPH context when destroying a
channel, so don't bother.

This commit should also fix kernel.org bug 39422, where the DRM channel
state was incorrectly being saved because we left PGRAPH FIFO access
enabled while running the ctxprog.

Signed-off-by: Ben Skeggs <d9f27fb07c1e9f131223ad827fa5179f3846c30b@redhat.com>

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs