[llvm] [libsycl] Add USM alloc & release funcs (PR #181120)

[Kseniya Tikhomirova via llvm-commits]

KseniyaTikhomirova wrote:

Hi @tahonermann, @dvrogozh, @sergey-semenov, @bader, @againull, @dm-vodopyanov,
I've created a new SYCL RT PR with initial USM alloc & free funcs impl. I will do an extra round of self-review this week but we can start reviewing this officially.

thanks.

https://github.com/llvm/llvm-project/pull/181120