platform: Add a weak API to return the max peripherals supported by SPMI

Add a weak API to return the max SPMI peripherals supported. By default
the max number of peripherals supported on the platform is 128.

Change-Id: I17f14c1783378a6aff49dfa32d8265990029391f
diff --git a/include/platform.h b/include/platform.h
index 2aa4c56..623473b 100644
--- a/include/platform.h
+++ b/include/platform.h
@@ -66,4 +66,5 @@
 int platform_is_msm8992();
 int boot_device_mask(int);
 uint32_t platform_detect_panel();
+uint32_t platform_get_max_periph();
 #endif