multilib: Tweak value of PN used for OVERRIDES

multilib: Tweak value of PN used for OVERRIDES

Currently, PN is used in overrides which is expanded to have a MLPREFIX. This
means and pn- overrides without the prefix would be ignored which is not what
is usually expected.

We noticed huge problems using poky-lsb with multilib since the per recipe
overrides were not applied. This adds in handling for PN with and without
the prefix. This should unbreak world-lsb builds on the autobuilder.

(From OE-Core rev: b4cf6631efd526728ac515ced1a7e578674ca6c1)

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