platform: correct the sequence for enabling DSI pixel clock

In the current implementation, the M,N,D values for DSI pixel clock is
set after setting the update RCG bit in DSI_PCLK_CMD_RCGR register.
This causes the dirty bits for M,N,D to be set in PCLK_CMD_RCGR causing
issues during handoff in kernel for DSI pixel clock. Update the sequence
to take care of this for multiple targets.

Change-Id: Ifcc53ca1787b710cd1a154738a7c1ccd472d22c7
4 files changed