[SYCL][Doc] Mark spec for prefetch extension as supported

[bader]

According to release notes the extension was implemented by
e7139b0,
0229456
and
b5d69df

[bader]

@KornevNikita, did I get it right that this extension is implemented?

[KornevNikita]

@bader should we have cts to mark it as supported?

[bader]

I believe we do not have such a requirement. @gmlueck?

[gmlueck]

I believe we do not have such a requirement. @gmlueck?

No, it is sufficient to have e2e tests in our own repo, and it looks like we did this in #11834.

However, there are two problems with the spec change in this PR:

• This extension is "experimental" not "supported", so it's in the wrong directory.
• The Status section text should be updated to note that it is "experimental". See the template for the right wording.

Also, I don't see any definition of the feature-test macro SYCL_EXT_ONEAPI_PREFETCH.

[bader]

However, there are two problems with the spec change in this PR:

• This extension is "experimental" not "supported", so it's in the wrong directory.
• The Status section text should be updated to note that it is "experimental". See the template for the right wording.

Fixed.

Also, I don't see any definition of the feature-test macro SYCL_EXT_ONEAPI_PREFETCH.

It's here -> https://github.com/intel/llvm/blob/sycl/sycl/source/feature_test.hpp.in#L100

[gmlueck]

Also, I don't see any definition of the feature-test macro SYCL_EXT_ONEAPI_PREFETCH.

It's here -> https://github.com/intel/llvm/blob/sycl/sycl/source/feature_test.hpp.in#L100

Oh, sorry. I just searched the "sycl/include" directory.