drm/msm/dp: add check for memory overflow while reading EDID modes

Add sanity check for memory overflow beyond PAGE_SIZE for reading
the EDID mode from debugfs node. Remove the horizontal and vertical
porch entries and add pixel clock to accommodate more modes
in the buffer.

Change-Id: I0bc760087c9c0a5f3eff2f89c44e9b2ab385359d
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>