msm: mdss: rename dsi phy version for msm8996 and sdm660

DSI phy v2 is used on msm8996 and sdm660. Update the phy
timing device node property to mention the correct DSI PHY
version. This will ensure that proper naming convention is
followed across msm8996 and sdm660 target.

Change-Id: Idd88110ddebf2dd38cfe375ac1bf3804ce4bb4d0
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>