Fix incorrect _ONEDPL_SYCL_USM_HOST_PRESENT usage in USM allocation helpers

[mmichel11]

__use_USM_allocations introduced in PR #1354 uses _ONEDPL_SYCL_USM_HOST_PRESENT to check if host memory support is present. However, this macro was renamed to _ONEDPL_SYCL_UNIFIED_USM_BUFFER_PRESENT in PR #1410, so the function always returns false. This causes incompatible scratch and result buffer paths to be taken in the code causing incorrect results and hangs.

This PR switches to use the correct macro here.

[julianmi]

@mmichel11 Thanks for raising this. I noticed several issues as well and am working on fixes for them. Namely:

1. Outdated macro as you suggested.
2. Empty scratch space allocation is unguarded when using USM host memory. This leads to runtime issues or bad_alloc.
3. The guards to support older compilers (Extend compiler support for the unified USM and buffer storage #1410) are missing.
4. __get_usm_host_or_buffer_accessor_ptr is not needed anymore.

I have a WIP branch here dev/julianmi/fix_reduce_1354 that will eventually address all four issues. So I think we can close this one.

[SergeyKopienko]

LGTM

[julianmi]

I believe #1503 supersedes this PR by including this macro fix and several other fixes.