plat/arm: mhu: make mhu driver generic

MHU doorbell driver requires arm platform specific
macro "PLAT_CSS_MHU_BASE".
Rename it to "PLAT_MHUV2_BASE", so that platforms other than arm
can use generic MHU doorbell driver.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
diff --git a/include/drivers/arm/css/css_mhu_doorbell.h b/include/drivers/arm/css/css_mhu_doorbell.h
index ecee563..e6f7a1b 100644
--- a/include/drivers/arm/css/css_mhu_doorbell.h
+++ b/include/drivers/arm/css/css_mhu_doorbell.h
@@ -12,7 +12,7 @@
 #include <lib/mmio.h>
 
 /* MHUv2 Base Address */
-#define MHUV2_BASE_ADDR		PLAT_CSS_MHU_BASE
+#define MHUV2_BASE_ADDR		PLAT_MHUV2_BASE
 
 /* MHUv2 Control Registers Offsets */
 #define MHU_V2_MSG_NO_CAP_OFFSET		0xF80