[SYCL] Build L0 v2 adapter by default

[igchor]

L0 v2 adapter is expected to be shipped as part of 2025.2 release.

Refactor params to configure.py into a single 'choice' param.

[pbalcer]

Please add a description of the new env variable to switch the adapter here: https://github.com/intel/llvm/blob/sycl/sycl/doc/EnvironmentVariables.md

Something like:

Enable ('1') or disable ('0') the use of a preview version of the Level Zero adapter, which features a redesigned architecture aimed at optimizing performance for different queue modes (immediate/batched, in-order/out-of-order). This version is expected to reduce runtime overhead. It requires a driver version of at least x.y.z. If you experience any performance or functional issues with this adapter enabled, please report them on GitHub, specifying the adapter used.

[igchor]

@intel/dpcpp-doc-reviewers could you please take a look?

[igchor]

@intel/llvm-gatekeepers this is ready to be merged, the CI failure is unrelated (there are no v2 tests running on PVC for now).

[igchor]

@sarnex @steffenlarsen, would you be able to merge this?