staging: panel: register driver after checking device

register the driver only if lcd or keypad has been enabled and if
both are disabled then just exit.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Acked-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>