mvebu: put u-boot images into image staging directory

Do not put the u-boot images into the kernel build directory as this directory
might get removed after kernel updates while the u-boot packages InstallDev
recipe is not getting re-executed because it is still considered current,
leading to image build failures later on due to missing u-boot images.

To ensure that built bootloader images persist over kernel version updates in
the buildroot, put them into the new STAGING_DIR_IMAGE directory.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

package/boot/uboot-mvebu/Makefile

@@ -31,8 +31,8 @@ UBOOT_TARGETS:= \
 	clearfog
 
 define Build/InstallDev
-	$(INSTALL_DIR) $(KERNEL_BUILD_DIR)/
-	$(CP) $(PKG_BUILD_DIR)/$(UBOOT_IMAGE) $(KERNEL_BUILD_DIR)/$(BUILD_VARIANT)-u-boot-spl.kwb
+	$(INSTALL_DIR) $(STAGING_DIR_IMAGE)
+	$(CP) $(PKG_BUILD_DIR)/$(UBOOT_IMAGE) $(STAGING_DIR_IMAGE)/$(BUILD_VARIANT)-u-boot-spl.kwb
 endef
 
 $(eval $(call BuildPackage/U-Boot))

target/linux/mvebu/image/Makefile

@@ -39,7 +39,7 @@ endef
 define Build/sdcard-img
 	ROOTFS_SIZE=$$(( $(CONFIG_TARGET_ROOTFS_PARTSIZE) * 1024 * 2 )); \
 	./gen_mvebu_sdcard_img.sh $@ \
-		"$(KDIR)/clearfog-u-boot-spl.kwb" \
+		"$(STAGING_DIR_IMAGE)/clearfog-u-boot-spl.kwb" \
 		c 32768 $@.boot \
 		83 $$ROOTFS_SIZE $(IMAGE_ROOTFS)
 endef