Fall back to use region instead of viewport to estimate drawing size

This fixes multiple games with graphic issue previously

1. MotoGP (Incorrect viewport)  Issue #702 
![screen00044](https://f.cloud.github.com/assets/3000282/756818/c3f68254-e649-11e2-8ca7-ad3706341822.jpg)

2. FF Type-0 (Dynamic Shadowing issue)  Issue #1272 
![screen00045](https://f.cloud.github.com/assets/3000282/756826/93396aea-e64a-11e2-9e03-3252c48491bd.jpg)

3. Castlevania The Dracula X Chronicles (Incorrect background size)
![screen00046](https://f.cloud.github.com/assets/3000282/756827/a2a3b3dc-e64a-11e2-88f4-117aa28cf7ac.jpg)