drm/msm/dsi-staging: remove redundant functions from dsi phy

This change removes the redundant functions defined in hw version
based modules by moving them into a common module.

Change-Id: Icae99b30faad6409b65f9831e3bb3d5f63a2512c
Signed-off-by: Govinda Rajulu Chenna <gchenna@codeaurora.org>