GBA2P with dual Monitor support (Patreon)

As it was requested so often, I added the support to output core/screen 2 via VGA.

HDMI can be set to Screen 1 in this mode, so each core has it's own screen.

Warning: as there was only space for a single buffer and the core cannot be halted in multiplayer mode("sync core to video"), as the GBAs would unsync and loose connection, so you might notice tearing. I apologize for that.  

The FPGA is so full, it took me 8 builds to even get an FPGA with timing closure. All elements(ALM, BRAM, DSP) are at roughly 90% usage.

I hope you forgive me if this is really the last change for this Core now, as any further work on it get's really tedious.

edit: 

release is available here: 

https://github.com/MiSTer-devel/GBA_MiSTer/tree/GBA2P

Have fun!