mediatek: mt7623: add back needed build steps for U7623 board

When reworking the BPi-R2 the mtk-mmc-img build step was removed
despite it was still needed to build the image for the UniElec U7623
board. Add it back for now until U7623 gets its facelift.

Signed-off-by: Daniel Golle <[email protected]>

target/linux/mediatek/image/mt7623.mk

@@ -113,6 +113,27 @@ endef
 TARGET_DEVICES += bananapi_bpi-r2
 
 
+define Build/mtk-mmc-img
+	rm -f [email protected]
+	mkfs.fat -C [email protected] $(BOOTFS_BLOCKS)
+
+	if [ -r $(STAGING_DIR_IMAGE)/$(UBOOT_TARGET)-preloader.bin ]; then \
+		./gen_mtk_mmc_img.sh emmc [email protected] \
+			$(STAGING_DIR_IMAGE)/$(UBOOT_TARGET)-preloader.bin; \
+		mcopy -i [email protected] [email protected] ::eMMCboot.bin; \
+	fi
+	mkenvimage -s $(UBOOT_ENVSIZE) -o $(STAGING_DIR_IMAGE)/$(UBOOT_TARGET)-uboot.env $(UBOOT_TARGET)-uEnv.txt
+	mcopy -i [email protected] $(STAGING_DIR_IMAGE)/$(UBOOT_TARGET)-uboot.env ::uboot.env
+	mcopy -i [email protected] $(IMAGE_KERNEL) ::uImage
+	./gen_mtk_mmc_img.sh sd $@ \
+		$(STAGING_DIR_IMAGE)/$(UBOOT_TARGET)-preloader.bin \
+		$(STAGING_DIR_IMAGE)/$(UBOOT_TARGET)-u-boot*.bin \
+		$(UBOOT_OFFSET) \
+		[email protected] \
+		$(IMAGE_ROOTFS) \
+		$(CONFIG_MTK_BOOT_PARTSIZE) \
+		$(CONFIG_TARGET_ROOTFS_PARTSIZE)
+endef
 
 define Build/scatterfile
 	./gen_scatterfile.sh $(subst mt,MT,$(SUBTARGET)) "$1" \