crypto/internal/fips140test: add feedback KDF ACVP tests

crypto/internal/fips140test: add feedback KDF ACVP tests

Adds ACVP test coverage for the SP 800-108r1 KDF feedback mode algorithm
based on the NIST spec:

  https://pages.nist.gov/ACVP/draft-celi-acvp-kbkdf.html

The HKDF-based implementation in our FIPS module fixes some parameters,
requiring tailoring of the advertised capability to match. Notably:

* We only support fixedDataOrder "after fixed data"
* We only support a counter length of 8 bits
* We only support empty IVs

No acvp_test.config.json update accompanies this support because the
ACVP tests for this algorithm aren't amenable to fixed data testing.

Updates #69642

Change-Id: I729e899377a64d2b613d6435241aebabeef93bca
Reviewed-on: https://go-review.googlesource.com/c/go/+/640016
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org>