drm: update VIA driver to 2.7.2

Add PCI DMA blitengine to VIA DRM
Add portability code for porting VIA to FreeBSD.
Sync via_drm.h with 3d driver

From: Thomas Hellstrom <unichrome@shipmail.org>, Eric Anholt <anholt@freebsd.org>
Signed-off-by: Dave Airlie <airlied@linux.ie>