drm/msm/dsi-staging: Add ULPS support for platforms with legacy dsi phy

This change adds ULPS feature support for ctrl ver 2.3. ULPS entry-exit
can be either through the DSI controller or the DSI PHY depending on
hardware variation. ULPS entry-exit will be requested through DSI
controller only if it is not handled in DSI PHY. This is required as for
some chipset, ulps ops can be present for both DSI controller version
as well as DSI PHY version.

Change-Id: I7ec7bf29ba2d64e2165dde68abad5e3762df0ce5
Signed-off-by: Ritesh Kumar <riteshk@codeaurora.org>