arm/dt: hammerhead: Increase command mode clock rate

Set command mode panel clock rate to 854.96MHz
This clock rate is within panel spec. Setting the value in device tree
avoids lower calculated clock value in driver. The transfer time from
mdp to panel is reduced and the overall system latency is improved.
The phy timings and the dsi-t clock settings are also adjusted accordingly

Bug: 10951729
Signed-off-by: sooduek.kim <sooduek.kim@lge.com>
Signed-off-by: Devin Kim <dojip.kim@lge.com>
Signed-off-by: Naseer Ahmed <naseer@codeaurora.org>