drm/vmwgfx: CRTC atomic state

Create and Add CRTC state.  We currently do not track any properties
or custom states so we can technically use the DRM helpers.  Creating
this code just to make potential future additions easier.

Most of the new code will be compiled but not enabled until
plane/connector state handling code is also in place.

This is the first of a series to enable atomic mode set for vmwgfx.

The atomic enabling effort was done in collaboration with Thomas
Hellstrom and the VMware Graphics Team.

Signed-off-by: Sinclair Yeh <syeh@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>