drm/vmwgfx: Use atomic helper function for dirty fb IOCTL

USe new atomic helper for dirty fb IOCTL which make use of damage
interface. Note that this is only done for STDU and SOU, for legacy
display unit still using old interface.

Signed-off-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>