ARM: dts: msm: Add panel dimension details for HX8394A 720p panel

Explicitly setting the physical dimensions of the panel helps
in correctly computing the DPI (dots per inch) settings. Add
this information for the HX8394A 720p panel based on the data
provided in the panel specification.

Change-Id: I502c763b64eae17912f476ac31895f82253f0ae0
Signed-off-by: Diego Wilson <dwilson@codeaurora.org>