[CRYPTO] tcrypt: Speed benchmark support for digest algorithms

This patch adds speed tests (benchmarks) for digest algorithms.
Tests are run with different buffer sizes (16 bytes, ... 8 kBytes)
and with each buffer multiple tests are run with different update()
sizes (e.g. hash 64 bytes buffer in four 16 byte updates).
There is no correctness checking of the result and all tests and
algorithms use the same input buffer.

Signed-off-by: Michal Ludvig <michal@logix.cz>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>