add basic SYCL support

src/pystencils/backend/kernelcreation/iteration_space.py

src/pystencils/backend/platforms/__init__.py

src/pystencils/backend/platforms/generic_cpu.py

src/pystencils/backend/platforms/sycl.py

src/pystencils/enums.py

src/pystencils/kernelcreation.py