[SYCL][FE] Add an attribute to annotate special sycl types

This is follow up task to address https://github.com/intel/llvm/pull/1877#discussion_r450213505 and probably https://reviews.llvm.org/D71016#inline-644645 .
To fix this we need to add an attribute to annotate SYCL types like accessor, sampler, image. It's much more reliable approach than declaration name, which introduces hard-coded dependency on exact symbol name in the runtime library.