staging: panel: Use better names for two defined values

Give DEFAULT_KEYPAD and DEFAULT_LCD defines better names,
so that their meaning is emphasized.

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>