anv/x11: Add present support

anv/x11: Add present support

The old DRI3 implementation just used CopyArea instead of present.  We
still don't support all the MST fancyness, but it should at least avoid
some copies and allow for.

v2 (Jason Ekstrand):
   - Better object cleanup and destruction
   - Handle the CONFIGURE_NOTIFY event and return OUT_OF_DATE when needed
   - Track dirtyness via IDLE_NOTIFY rather than interating through the
     images sequentially