Drop the deprecated drmP.h header from nouveau_drv.h.
Fix fallout in other parts of the driver.

Build tested using allmodconfig and allyesconfig.
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: nouveau@lists.freedesktop.org
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>