fbdev/stifb: Allocate fb_info instance with framebuffer_alloc()

Allocate stifb's instance of fb_info with framebuffer_alloc(). This
is the preferred way of creating fb_info with associated driver data
stored in struct fb_info.par. Requires several, but minor, changes
through out the driver's code.

The intended side effect of this patch is that the new instance of
struct fb_info now has its device field correctly set to the parent
device of the STI ROM. A later patch can detect if the device is the
firmware's primary output. It is also now correctly located within
the Linux device hierarchy.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Helge Deller <deller@gmx.de>
Reviewed-by: Helge Deller <deller@gmx.de>
Signed-off-by: Helge Deller <deller@gmx.de>