msm: mdss: properly handle dsi phy regulator for dual dsi case

In dual dsi case, if we do DSI PHY sw reset for one DSI controller
then it will reset the DSI PHY regulator also. Since DSI PHY
regulator is shared among both the DSI controllers, it might cause
side effects on the other DSI controller if that is active. So only
reset DSI PHY lane and PHY HW as when one of the DSI controller is
still in active state. Also avoid reconfiguring DSI PHY regulator in
dual dsi case if the other DSI controller is active.

Change-Id: I5ad1251c89e8ad3f521c4e5c11607494e14143cf
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>