license: Fix directory layout issues

There are several issues:

a) pointless empty directories were being created as a path wasn't
   fixed in a previous commit
b) SSTATE_PKGARCH wasn't being captured into the task signature
   since it is in the ignore list by default. We want to capture
   the absolute value, not the dependencies
c) with those issues fixed, cross/native issues became apparent so
   those need to be fixed too.

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