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/drivers/arm/gicv3.h b/include/drivers/arm/gicv3.h
index c52fe48..4548a87 100644
--- a/include/drivers/arm/gicv3.h
+++ b/include/drivers/arm/gicv3.h
@@ -349,5 +349,7 @@
 void gicv3_its_save_disable(uintptr_t gits_base, gicv3_its_ctx_t * const its_ctx);
 void gicv3_its_restore(uintptr_t gits_base, const gicv3_its_ctx_t * const its_ctx);
 
+unsigned int gicv3_get_running_priority(void);
+
 #endif /* __ASSEMBLY__ */
 #endif /* __GICV3_H__ */