drm: bridge: dw-hdmi: Enable CSC even for DVI

If the input pixel format is not RGB, the CSC must be enabled in order to
provide valid pixel to DVI sinks.
This patch removes the hdmi only dependency on the CSC enabling.

Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170303172007.26541-4-laurent.pinchart+renesas@ideasonboard.com