intel_idle: stop using driver_data for static flags

The commit, 4202735e
(cpuidle: Split cpuidle_state structure and move per-cpu statistics fields)
observed that the MWAIT flags for Cn on every processor to date were the
same, and created get_driver_data() to supply them.

Unfortunately, that assumption is false, going forward.
So here we restore the MWAIT flags to the cpuidle_state table.
However, instead restoring the old "driver_data" field,
we put the flags into the existing "flags" field,
where they probalby should have lived all along.

This patch does not change any operation.

This patch removes 1 of the 3 users of cpuidle_state_usage.driver_data.
Perhaps some day we'll get rid of the other 2.

Signed-off-by: Len Brown <len.brown@intel.com>