This optimises the drm code to not do put_user() on memory the kernel
allocated and then mmap-installed to userspace, but instead makes it use
the kernel virtual address directly instead. 

From: Arjan van de Ven <arjanv@redhat.com>
Signed-off-by: Dave Airlie <airlied@linux.ie>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>