drm/msm/dsi-staging: update enable and reset logic

This patch adds appropriate memory barriers and clock enables
to the DSI enable and reset routines, and moves the DSI panel
disable call to match the panel enable sequence.

CRs-Fixed: 2019299
Change-Id: I2d9e7a284220437b70395e070cd049afb5d51f08
Signed-off-by: Clarence Ip <cip@codeaurora.org>