classes/populate_sdk_ext: tweak reporting of workspace exclusion
If you have a local workspace layer enabled when building the
extensible SDK, we explicitly exclude that from the SDK (mostly because
the SDK has its own for the user to use). Adjust the message we print
notifying the user of this so it's clear that we're excluding it from
the SDK, and scale it back from a warning to a note printed with
bb.plain().
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
