[media] omap: Fix Kconfig dependencies on OMAP2

Resolves the following warning that appears with allmodconfig on -arm:
	warning: (VIDEO_OMAP2_VOUT && DRM_OMAP) selects OMAP2_DSS which has unmet direct dependencies (HAS_IOMEM && ARCH_OMAP2PLUS)

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>