[AGPGART] allow drm populated agp memory types cleanups

Fix whitespace, braces, use kzalloc().

Cc: Dave Airlie <airlied@linux.ie>
Cc: Thomas Hellstrom <thomas@tungstengraphics.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Jones <davej@redhat.com>