fbdev: omap/lcd: Staticize non-exported lcd_panel structs

None of the lcd_panel structs defined by the OMAP LCD drivers are
referenced outside of their compilation unit. Follow best practices and
mark them as static.

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>