kbuild: add image_name to no-sync-config-targets

'make image_name' needs include/config/auto.conf to show the correct
output because KBUILD_IMAGE depends on CONFIG options, but should not
attempt to resync the configuration.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -264,7 +264,8 @@ no-dot-config-targets := $(clean-targets) \
 			 $(version_h) headers headers_% archheaders archscripts \
 			 %asm-generic kernelversion %src-pkg dt_binding_check \
 			 outputmakefile
-no-sync-config-targets := $(no-dot-config-targets) %install kernelrelease
+no-sync-config-targets := $(no-dot-config-targets) %install kernelrelease \
+			  image_name
 single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.s %.symtypes %/
 
 config-build	:=