base.bbclass: Update the preferred_ml_updates

base.bbclass: Update the preferred_ml_updates

When processing the blacklists, we should avoid cross-canadian packages, as they
will not have any multilib prefixes to expand.

Similarly look for "virtual/nativesdk-" in addition to the existing "nativesdk-".
These items should also be ignored.

Finally, in order to avoid undeterministic variable key expansion, such as:

MYVAR = "foo"

PREFERRED_PROVIDER_${MYVAR} = "bar"
PREFERRED_PROVIDER_foo = "foobar"

during the multilib processing of PREFERRED_VERSION and PREFERRED_PROVIDER,
the code was changed to rename the variable key, to the final key.  This along
with the existing code avoids the problems.

Signed-off-by: Mark Hatle <mark.hatle@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>