x86/intel_rdt: Check monitor group vs control group membership earlier

A task can only be moved between monitor groups if both groups belong to
the same control group. This is checked fairly late however: by that time
we already have appended a task_work() callback.

Check the validity of the move before getting anywhere near task_work
callbacks.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>