platform: Add function to detect the panel and pick up corresponding DT

For 8909, add function to detect the panel as HD/qHD based on the value
read from a register and update the bits 11:12 of the hlos_subtype
accordingly, so as to pick the correct DT.

Change-Id: Ic2e3b053c6423afe5c6604c3d6b84fd0a54dc027
4 files changed