[media] omap3isp: Don't include <plat/cpu.h>

The plat/*.h headers are not available to drivers in multiplatform
kernels. As the header isn't needed, just remove it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Sakari Ailus <sakari.ailus@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>