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
diff --git a/platform/init.c b/platform/init.c
index 4783eba..aeb4f20 100644
--- a/platform/init.c
+++ b/platform/init.c
@@ -135,3 +135,8 @@
 {
 	return ((val & 0x3E) >> 1);
 }
+
+__WEAK uint32_t platform_detect_panel()
+{
+	return 0;
+}