image-commands: make use of gzip-libdeflate

Now that we provide a better gzip compression tool we can make use of
it whereever gzip is used. Change Build/gzip command to new gzip-libdeflate
compressor.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>

include/image-commands.mk

@@ -298,7 +298,7 @@ define Build/fit
 endef
 
 define Build/gzip
-	gzip -f -9n -c $@ $(1) > $@.new
+	$(STAGING_DIR_HOST)/bin/gzip-libdeflate -f -12 -c $@ $(1) > $@.new
 	@mv $@.new $@
 endef