staging: panel: Refactor LCD init code

Rework lcd_init method to make it a little bit more clear about
the precedence of the params, move LCD geometry and pins layout
to the LCD struct and thus make the LCD-related module params
effectively read-only.

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>