Recent changes assumed OpenCL 2.0 platform. This adds a check to see if
we are compiling on an OpenCL 2.0 platform.
Patch was tested on:
* AMD Radeon Pro WX 7100 with amdgpu-pro-19.50-1011208-ubuntu-18.04 drivers
* AMD Vega 64 with amdgpu-pro-20.10-1048554-ubuntu-18.04 drivers
* AMD RX 5700 with amdgpu-pro-20.10-1048554-ubuntu-18.04 drivers
Reviewed By: Brecht van Lommel
Differential Revision: https://developer.blender.org/D7637