Rename "fbdev" -> "sunxifb" and update man page

As there is no way for the hardware specific bits to be accepted
in xf86-video-fbdev, we need a new driver with its own name.
Move driver private data into a separate header file

It is going to be included by multiple different source files.
Added supplementary wrapper functions for sunxi display controller ioctls

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".
Support for sunxi hardware cursor

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.