[SYCL] Change SYCL version according to standard (#114790)
Version of SYCL was changed according to the latest agreement:
The lower 2 digits are not formally specified, but we plan to use these
to identify the month in which we submit the specification for
ratification, which is similar to the C++ macro __cplusplus.
Since the SYCL 2020 specification was submitted for ratification in
December of 2020, the macro's value is now 202012 for SYCL 2020.
see PR for details
https://github.com/KhronosGroup/SYCL-Docs/pull/634
