mdss: display: edp continuous splash support

Both edp main link clock and pixel clock are source from PLL.
This patch add edp clock nodes into system clock tree so that
both main link clock and pixel clock are configured properly
to support different panels with different resolution. Edp
related clocks handoff from bootloader are supported.

Change-Id: I6e4096beb9bff0d39f4f850bbc6d2157ac42e524
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>