drm: bridge: dw-hdmi: Move CSC configuration out of PHY code

The color space converter isn't part of the PHY, move its configuration
out of PHY code.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170303172007.26541-3-laurent.pinchart+renesas@ideasonboard.com