[SYCL] Implement SYCL address space attributes handling

Default address space (applies when no explicit address space was
specified) maps to generic (4) address space.

Added SYCL named address spaces `sycl_global`, `sycl_local` and
`sycl_private` defined as sub-sets of the default address space.

Static variables without address space now reside in global address
space when compile for SPIR target, unless they have an explicit address
space qualifier in source code.

Differential Revision: https://reviews.llvm.org/D89909