[SYCL][DOC] Update sycl_ext_oneapi_prefetch

[KornevNikita]

The compiler treats such code:

prefetch(ptr, 8)

as call to void prefetch(void ptr, Properties properties = {}), instead of void prefetch(T ptr, size_t count, Properties properties = {});

Adding constraints to avoid this.

[KornevNikita]

Not sure how this constraint should be added. Is it okay to add just like Note?
Or it should be added as a comment in API example / Constraints string in every method description?

[gmlueck]

Or it should be added as a comment in API example / Constraints string in every method description?

It should be added as a Constraints: paragraph on every function. For example, see how the joint_prefetch functions all have a paragraph:

Constraints: Available only if sycl::is_group_v<std::decay_t> is true.

The Constraints: paragraph should precede Preconditions: and Effects:.