FramebufferManager: Support stereoscopic EFB format changes.
PixelShaderCache: Support stereoscopic EFB format changes.
FramebufferManager: Use a separate layer variable.
Cosmetics.
Merge pull request #1748 from Armada651/stereo-format

FramebufferManager: Support stereoscopic EFB format changes.
FramebufferManager: Copy all EFB layers to the XFB framebuffer.
OGL: Support stereoscopic XFB blit to screen.
FramebufferManagerBase: Only allocate one layer for Real XFB.
GeometryShaderCache: Cosmetics.
FramebufferManager: Copy all EFB layers to the XFB.
D3D: Support stereoscopic XFB blit to screen.
VideoConfig: Turn off stereoscopy when Real XFB is enabled.