drm/msm/dsi-staging: add P/N swap support for DSI PHY

Add P/N support for DSI PHY. P/N lane swap information will parse
from devicetree and config to DSI PHY when enabled.

Change-Id: Icfcb8e3bb09422ad8aa917653b7c8ad02faa02ea
Signed-off-by: Xiaowen Wu <wxiaowen@codeaurora.org>