drm/msm/dp: add support for device tree parser

Add a module that can be called by DisplayPort driver to
parse all the device tree related data. Parse the device
tree data related to DisplayPort and populate it into the
data structures which can be used by the DisplayPort driver.
The device tree data may include register addresses, clock,
regulator, pin control, gpio etc data.

This implementation is based on a snapshot of the DisplayPort
driver as of this commit 0f175f91a849b717be ("msm: mdss: dp:
fix HDCP 1.x state transitions") on kernel-4.4.

Change-Id: I4b1517d8930ff15e4c00e15cd21b8a9ede1135bc
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>