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The modern desktops may use ARGB cursors. As the current
sunxi display controller support code can't handle this
type of cursor yet, the X server fallbacks to a software
cursor which is not visible under layers and ruining user
experience.

This patch adds empty implementations for "UseHWCursorARGB"
and "LoadCursorARGB" functions which just return error for
now (so that the X server still fallbacks to software cursor).
However we also introduce callback functions responsible for
notifying the DRI2 code about enabling/disabling the use of
hardware cursor. So that now hardware overlays are disabled
when switching to software cursor and re-enabled again when
switching back to hardware cursor.
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>

Testing with gnome-shell revealed a problem. We need to migrate
pixmaps into UMP buffers in order to allow the GLESv2 based
compositing manager to actually access the content of redirected
windows, rendered by X11 applications into offscreen pixmaps.

Just to make sure that we don't add any unneeded overhead for 2D
(neither extra CPU cycles nor the increase for unrelated pixmaps
memory footprint), a hash table (currently uthash [1]) is used
for connecting DRI2-enabled pixmaps with UMP buffers. The lookups
are only performed on DRI2 buffer creation and pixmap destruction.

1. http://troydhanson.github.com/uthash/

Reported-by: Michal Suchanek <hramrach@gmail.com>
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>

The driver can use sunxi display controller layers for fully visible
windows, avoiding expensive memory copy.