mvebu: image: rework uDPU-firmware recipe

Tar has ability to change current dir, so use that instead additional
command invocation. Also being here, change tar arguments to make final
archive reproducible.

Cc: Scott Roberts <[email protected]>
Signed-off-by: Tomasz Maciej Nowak <[email protected]>

target/linux/mvebu/image/Makefile

@@ -70,9 +70,15 @@ define Build/uDPU-firmware
 	(rm -fR $@-fw; mkdir -p $@-fw)
 	$(CP) $(BIN_DIR)/$(IMAGE_PREFIX)-initramfs.itb $@-fw/recovery.itb
 	$(CP) [email protected] $@-fw/boot.scr
-	(cd $(TARGET_DIR); $(TAR) -cvzf $@-fw/rootfs.tgz .)
-	(cd [email protected]; $(TAR) -cvzf $@-fw/boot.tgz .)
-	(cd $@-fw; $(TAR) -cvzf $(KDIR_TMP)/$(IMAGE_PREFIX)-firmware.tgz .)
+	$(TAR) -cvzp --numeric-owner --owner=0 --group=0 --sort=name \
+		$(if $(SOURCE_DATE_EPOCH),--mtime="@$(SOURCE_DATE_EPOCH)") \
+		-f $@-fw/rootfs.tgz -C $(TARGET_DIR) .
+	$(TAR) -cvzp --numeric-owner --owner=0 --group=0 --sort=name \
+		$(if $(SOURCE_DATE_EPOCH),--mtime="@$(SOURCE_DATE_EPOCH)") \
+		-f $@-fw/boot.tgz -C [email protected] .
+	$(TAR) -cvzp --numeric-owner --owner=0 --group=0 --sort=name \
+		$(if $(SOURCE_DATE_EPOCH),--mtime="@$(SOURCE_DATE_EPOCH)") \
+		-f $(KDIR_TMP)/$(IMAGE_PREFIX)-firmware.tgz -C $@-fw .
 endef
 
 define Device/Default