iOS: add GLES 3.0 support

For some reason GL_OES_packed_depth_stencil ext not present in GLES 3.0 on iOS. Therefore framebuffer was configured for Tegra devices. I skipped this check. 
Also on iOS not need call gl3stubInit() so i defined this as macros (maybe it bad way).

Tested on iPhone 4S (iOS 7.0.4, GLES 2.0, Jailbreak) and iPad Air (iOS 7.0.4, GLES 3.0, Without jail).