synquacer: Add MHU driver

Add Message Handling Unit (MHU) driver used to communicate among
Application Processors (AP) and System Control Processor (SCP).

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
diff --git a/plat/socionext/synquacer/include/platform_def.h b/plat/socionext/synquacer/include/platform_def.h
index aa15234..07db2b6 100644
--- a/plat/socionext/synquacer/include/platform_def.h
+++ b/plat/socionext/synquacer/include/platform_def.h
@@ -54,6 +54,8 @@
 #define SQ_SYS_TIMCTL_BASE		0x2a810000
 #define PLAT_SQ_NSTIMER_FRAME_ID	0
 
+#define PLAT_SQ_MHU_BASE		0x45000000
+
 #define SQ_BOOT_CFG_ADDR			0x45410000
 #define PLAT_SQ_PRIMARY_CPU_SHIFT		8
 #define PLAT_SQ_PRIMARY_CPU_BIT_WIDTH		6