mdss: display: expose panel parameters through framebuffer API

Panel porch values and pixel clock can be used to calculate the refresh
rate from user space. Assign these values with information from panel
driver.

Change-Id: I29995d27904e50892d72de5e8c7dd39285f9d421
Signed-off-by: Adrian Salido-Moreno <adrianm@codeaurora.org>