viafb: remove ioctls which break the framebuffer interface

The ioctls VIAFB_SET_DEVICE, VIAFB_SET_DEVICE_INFO and
VIAFB_SET_SECOND_MODE are removed because they prevent a clean
framebuffer driver because they modify the hardware and/or the
internal structures.
There are no known applications using these ioctls so no breakage is
expected. Additionaly the main functionality was duplicating the
framebuffer interface so there really should not exist any user.
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Cc: Joseph Chan <JosephChan@via.com.tw>