1. Add complex factor and targetQp to modify rate control.

Signed-off-by: zoominla <zoominla@gmail.com>
Commit some missing modify.
1. Add reading Qp values of pass1.
2. Remove Complexity ratio switch.
Update rate control method.
Add decrease bitrate function in 2-pass encoding.

Signed-off-by: zoominla <zoominla@gmail.com>