drm/msm/dsi-staging: Add a new bridge DTS property support

Parse the "qcom,qcom,mdss-dsi-ext-bridge" DTS property instead
of the old mdss-dsi-ext-bridge-mode. This node defines the port
reg value, can match the port setting in dsi display. Now use
this property to define bridge setting, if it was not set, it
should be a DSI panel.

Change-Id: Ibb514b541f8c1c413b365c48fdf95247867c4f45
Signed-off-by: Yuan Zhao <yzhao@codeaurora.org>