ANDROID: Move SCX_OPS_DISABLING VH inside the scx_fork_rwsem section

We found a stability issue in current code of scx_ops_disable_workfn
founction. When SCX_OPS_DISABLING VH is invoked, system may keeps
forking fair tasks. In this circumstances, if scx_ops_disable_workfn
is blocked by scx_fork_rwsem, it may never running again because the
task who invoking scx_ops_disable_workfn is scx task.

So we move the SCX_OPS_DISABLING VH inside scx_fork_rwsem section.

This patchset ensures that if the scx task who invoking
scx_ops_disable_workfn is blocked by scx_fork_rwsem, the system will
not produce fair task. This can avoid the stability issue caused in
scx disabling process.

Bug: 439095466

Change-Id: I16e67e868d8ba1a7f14309eab64b7d5d781e5ca9
Signed-off-by: ZhiFeng Gao <gaozhifeng@oppo.com>