crypto: tcrypt - add multi buf ahash jiffies test

The multi buffer concurrent requests ahash speed test only
supported the cycles mode. Add support for the so called
jiffies mode that test performance of bytes/sec.

We only add support for digest mode at the moment.

Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>