multilib: Use BPN instead of PN for style like lib${PN}

multilib: Use BPN instead of PN for style like lib${PN}

When supporting multilib, ${PN} will be extended with MLPREFIX. However
if a package name contains ${PN} with styles like lib${PN}, such
extension will cause error. Use BPN in this case.

Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>