Patch SDL2 for System 6 24bit ROM

[rickyzhang82]

The 24bit ROM doesn't invoke video driver control. Therefore, a manual step is required to add a black & white palette for guest_surface in SDL2.

Please check out the screen cast here.

Also, some other minor changes:

• Fix indentions.
• Move RAM, ROM debug message. The guest OS doesn't populate until init is done. So move it to a better place to show the value.
• Add comment to explain the magic number used in the 24 bit ROM frame buffer mapping.

Happy Independence Day!