staging: panel: Start making module params read-only

Start decoupling module params from the actual device state,
both for lcd and keypad, by keeping the params read-only
and moving the device state to related structs.

Signed-off-by: Mariusz Gorski <marius.gorski@gmail.com>
Acked-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>