amlogic: Move MHU code to common directory

The MHU code is shared between all the supported platforms. Move it to
the common directory instead.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>
Change-Id: Iaf53122866eae85c13f772927d16836dcfa877a3
diff --git a/plat/amlogic/gxl/platform.mk b/plat/amlogic/gxl/platform.mk
index 5c8206c..b4f2a90 100644
--- a/plat/amlogic/gxl/platform.mk
+++ b/plat/amlogic/gxl/platform.mk
@@ -32,7 +32,7 @@
 				${AML_PLAT_COMMON}/aarch64/aml_helpers.S	\
 				${AML_PLAT_SOC}/gxl_bl31_setup.c	\
 				${AML_PLAT_COMMON}/aml_efuse.c		\
-				${AML_PLAT_SOC}/gxl_mhu.c		\
+				${AML_PLAT_COMMON}/aml_mhu.c		\
 				${AML_PLAT_SOC}/gxl_pm.c		\
 				${AML_PLAT_COMMON}/aml_scpi.c		\
 				${AML_PLAT_SOC}/gxl_sip_svc.c		\