plat: marvell: armada: Move definition of mrvl_flash target to common marvell_common.mk file

Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: If545b3812787cc97b95dbd61ed51c37d30c5d412
diff --git a/plat/marvell/armada/common/marvell_common.mk b/plat/marvell/armada/common/marvell_common.mk
index e5ee710..a43bb5c 100644
--- a/plat/marvell/armada/common/marvell_common.mk
+++ b/plat/marvell/armada/common/marvell_common.mk
@@ -96,3 +96,6 @@
 
 .PHONY: mrvl_bootimage
 mrvl_bootimage: $(BUILD_PLAT)/$(BOOT_IMAGE)
+
+.PHONY: mrvl_flash
+mrvl_flash: $(BUILD_PLAT)/$(FLASH_IMAGE)