drm tiled monitor support (not hiding in kernel)

[Dave Airlie]

So I believe attempts to hide the DP MST tiled monitors in the kernel,
are a path to failure, so I've resurrected my previous code to just
create a tile property on the connectors for userspace to key off.

The contents of the tile blob are ABI, and I expect it to be
parsed by a fair few userspace projects.

So far I've ported a few pieces of GNOME to using it and posted
patches for that to their lists,

The X server should use this for make better XINERAMA info,
but otherwise drivers should pass the TILE property through
to the clients, as it contains nothing kernel specific.

Dave.