Missing radeonfb_setup

Simple patch to the new radeon fb driver to make it set modes/resolutions,
and take the other parameters.
Extracted some code from the matroxfb driver. Added radeonfb_setup function.

Also, with the new fbdev driver and with or without this little fix, tested in -test8 and
-test9 I cannot get my console framebuffer back when I switch from X, system working ok,
but the console is distorted. I have a Radeon 9600 Pro.

Salu2.

Javier Villavicencio.