include: Add function declaration to detect platform as 8956

Add function declaration to detect the platform as 8956.

Change-Id: I8e8f5997fb951b40c1a4b09800713e2d25235a83
diff --git a/include/platform.h b/include/platform.h
index 3cb7f2f..0c59056 100644
--- a/include/platform.h
+++ b/include/platform.h
@@ -65,6 +65,7 @@
 int platform_is_msm8939();
 int platform_is_msm8909();
 int platform_is_msm8992();
+int platform_is_msm8956();
 int boot_device_mask(int);
 uint32_t platform_detect_panel();
 uint32_t platform_get_max_periph();