build: target_config_lib: do not build unused packages for targets without opkg (#2051)

Normally, we build all nonshared packages (which includes all kernel
modules) to generate an opkg feed for later package installations by
users. On targets without opkg, this just wastes time - disable it.

(cherry picked from commit b3edfd29)

scripts/target_config_lib.lua

@@ -139,6 +139,7 @@ lib.check_devices()
 if not lib.opkg then
 	lib.config('SIGNED_PACKAGES', false)
 	lib.config('CLEAN_IPKG', true)
+	lib.config('ALL_NONSHARED', false)
 	lib.packages {'-opkg'}
 end
 

targets/generic

@@ -40,7 +40,7 @@ config('PACKAGE_kmod-jool', false) -- fails to build
 config('BUSYBOX_CUSTOM', true)
 config('BUSYBOX_CONFIG_FEATURE_PREFER_IPV4_ADDRESS', false)
 
-config('PACKAGE_ATH_DEBUG', true)
+try_config('PACKAGE_ATH_DEBUG', true)
 
 try_config('TARGET_SQUASHFS_BLOCK_SIZE', 256)