lxfb: fix incorrect __init annotation

WARNING: vmlinux.o(.data+0x196e8): Section mismatch in reference from the
variable lxfb_driver to the function .init.text:lxfb_probe() The variable
lxfb_driver references the function __init lxfb_probe()

This changes lxfb_probe and friends to use __devinit, and also adds
__devexit to lxfb_remove.

Signed-off-by: Andres Salomon <dilinger@queued.net>
Cc: Jordan Crouse <jordan.crouse@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>