OMAPDSS: add missing sizes.h includes

When compiling on x86, we get compilation errors for dss.c and dispc.c:

drivers/video/omap2/dss/dispc.c:126:11: error: ‘SZ_4K’ undeclared here
(not in a function)

include <linux/sizes.h> to fix compilation.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>