ANDROID: GKI: sched: put back the cpu_capacity_inverted variable

In commit 8517d739 ("sched/fair: Remove capacity inversion
detection"), the cpu_capacity_inverted was removed from struct rq.  Add
it back to preserve the abi and comment that it's not valid anymore.

Note, due to external modules using internal structures like this, it's
going to be "tricky" for them to even notice this has changed.  Their
build systems are going to have "fun" with this...

Bug: 161946584
Fixes: 8517d739 ("sched/fair: Remove capacity inversion detection")
Change-Id: I2b41b3ba2eb23fbb33ff872915a5e481640d0cc4
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>