GIC: Add API to get running priority

Document the API in separate platform interrupt controller API document.

Change-Id: If18f208e10a8a243f5c59d226fcf48e985941949
Co-authored-by: Yousuf A <yousuf.sait@arm.com>
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>
diff --git a/include/plat/common/platform.h b/include/plat/common/platform.h
index e189f64..7468352 100644
--- a/include/plat/common/platform.h
+++ b/include/plat/common/platform.h
@@ -70,6 +70,11 @@
 				     uint32_t security_state);
 
 /*******************************************************************************
+ * Optional interrupt management functions, depending on chosen EL3 components.
+ ******************************************************************************/
+unsigned int plat_ic_get_running_priority(void);
+
+/*******************************************************************************
  * Optional common functions (may be overridden)
  ******************************************************************************/
 uintptr_t plat_get_my_stack(void);