mdss: dp: fix the NVID parameter calculation for Display Port

The NVID programming for Display Port needs to be set to twice
the 'n' divider of the pixel clock RCG for 5.4 GHz link rate.
Add change to take care of this in Display Port driver.

Change-Id: Ied31f67372d9738e96d1d908acd96a02b82d4630
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>