target-sdk-provides-dummy: skip package_qa_multilib check

target-sdk-provides-dummy: skip package_qa_multilib check

The rprovides of target-sdk-provides-dummy don't be updated with
multilib, so it fails package_qa_multilib check. Because
target-sdk-provides-dummy doesn't install any file to sysroot, it is
safe to skip package_qa_multilib check for target-sdk-provides-dummy.

Remove ${MLPREFIX}target-sdk-provides-dummy from TOOLCHAIN_TARGET_TASK
at same time in populate_sdk_base.bbclass.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>