drm: dp helper: Add DP test sink CRC definition.

This address will be used to verify panel CRC for test and
validation purposes.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@gmail.com>
[danvet: Fix whitespace fail.]
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>