sched/eas: Check a task has a fitting cpu when updating misfit

If a misfit task is affined to a subset of the possible cpus, we need
to verify that one of these cpus can fit it. Otherwise the load balance
code will continuously trigger needlessly leading to balance_interval to
increase in return and eventually end up with a situation where real
imbalances take a long time to address because of this impossible
imbalance situation.

Signed-off-by: Qais Yousef <qais.yousef@arm.com>