drm/bridge/synopsys: Add MIPI DSI host controller bridge

Add a Synopsys Designware MIPI DSI host DRM bridge driver, based on the
Rockchip version from rockchip/dw-mipi-dsi.c with phy & bridge APIs.

Signed-off-by: Philippe CORNU <philippe.cornu@st.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1500277223-29553-5-git-send-email-philippe.cornu@st.com