drm: bridge: dw-hdmi: Move the driver to a separate directory.

The driver is already made of 5 separate source files. Move it to a
newly created directory named synopsys where more Synopsys bridge
drivers can be added later (for the DisplayPort controller for
instance).

Suggested-by: Jose Abreu <Jose.Abreu@synopsys.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170303172007.26541-10-laurent.pinchart+renesas@ideasonboard.com