malta: mark as source-only to avoid wasting build resources

The le64 and be64 subtargets do not share a package architecture with
any other targets, so they are pretty wasteful for a development-only
target.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/malta/Makefile

@@ -12,7 +12,7 @@ CPU_TYPE:=24kc
 SUBTARGETS:=le be le64 be64
 INITRAMFS_EXTRA_FILES:=
 MAINTAINER:=Florian Fainelli <florian@openwrt.org>
-FEATURES:=ramdisk
+FEATURES:=ramdisk source-only
 
 KERNEL_PATCHVER:=4.4