realtek: Makefile: add rt-loader-standalone and zynsig recipes

This adds the build recipes for rt-loader-standalone and zynsig to the
Makefile. The recipes are required for the upcoming ZyXEL GS1920 series.

Signed-off-by: Andreas Böhler <dev@aboehler.at>
Link: https://github.com/openwrt/openwrt/pull/20439
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/realtek/image/Makefile

@@ -37,6 +37,12 @@ define Build/rt-loader-no-uimage
         mv "$@.new" "$@"
 endef
 
+define Build/rt-loader-standalone
+	$(MAKE) all clean -C rt-loader CROSS_COMPILE="$(TARGET_CROSS)" \
+		FLASH_ADDR=$(FLASH_ADDR) KERNEL_IMG_OUT="$@.new" BUILD_DIR="$@.build"
+	mv "$@.new" "$@"
+endef
+
 define Build/zyxel-vers
        ( echo VERS;\
        for hw in $(ZYXEL_VERS); do\
@@ -102,6 +108,12 @@ define Build/linksys-image
 	mv $@.new $@
 endef
 
+define Build/zynsig
+	$(STAGING_DIR_HOST)/bin/zynsig -i $@ \
+		-o $@.new
+	mv $@.new $@
+endef
+
 define Device/Default
   PROFILES = Default
   KERNEL := \