support GL_EXT_YUV_target on SKL
Submitted by Dongseong Hwang
Assigned to Ian Romanick
Intel Skylake Gen9 whitepaper mentions "Texture samplers now natively support an NV12 YUV format for improved surface sharing between compute APIs and media fixed function units." https://software.intel.com/sites/default/files/managed/c5/9a/The-Compute-Architecture-of-Intel-Processor-Graphics-Gen9-v1d0.pdf
Intel Android 3D driver supports GL_EXT_YUV_target on Skylake. However, Mesa doesn't support GL_EXT_YUV_target on Skylake.