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Should be useful for better performance when moving windows
and scrolling on the devices without a dedicated 2D hardware
accelerator (Allwinner A13).
Signed-off-by: Siarhei Siamashka <siarhei.siamashka@gmail.com>

This initial G2D support code can speed up moving windows in XFCE. Currently
disabled by default, but can be enabled by editing /etc/X11/xorg.conf and
adding the following line to the "Device" section:

        Option          "AccelMethod" "G2D"
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.

Hardware cursor is necessary because it is also visible on
top of sunxi disp layers, while software cursor is not.

FIXME: there is one minor problem with negative cursor
positions. The hardware does not support them, so such
positions are just set to 0 for now. In the future this
can be solved better by changing the cursor picture and
showing only the parts which are visible on screen.

Note: the header file "sunxi_disp_ioctl.h" is GPL licensed. So until
it is gets a MIT/X11 replacement, the DDX driver is GPL licensed as
a whole. The individual source files still have their own license.
Also in order to avoid any possible confusion, the MIT/X11 license
header from COPYING has been added to "fbdev.c" and "fbdev_priv.h".

It is going to be included by multiple different source files.