poky: Enable spdx manifests by default

We're now in a position to enable SPDX manifests by default, do this
for poky.

(From meta-yocto rev: 511f2f60cc2637ebc06049f58acb4f68562b2fce)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-poky/conf/distro/poky.conf

@@ -69,3 +69,6 @@ INIT_MANAGER ?= "${POKY_INIT_MANAGER}"
 
 # We need debug symbols so that SPDX license manifests for the kernel work
 KERNEL_EXTRA_FEATURES:append = " features/debug/debug-kernel.scc"
+
+# Enable creation of SPDX manifests by default
+INHERIT += "create-spdx"