Properly scale FBOs on copy to output.

Fixes Tales of Destiny 2 and Star Ocean when buffered rendering is on.
Should only draw the top left 480x272.
These are in gstate_c, don't need externs.
Never use textureFullAlpha w/ framebuffer textures.
Actually, mark BGR5650 as full alpha.
Merge pull request #2569 from unknownbrackets/fbo-scale

Copy only a screen's worth of pixels from FBO to output