Use test_set_step() in loop in cf_hmac test
Use test_set_step() in loop in cf_hmac test

We only have a single integer available for two nested loops, but the loop
sizes are small enough compared to the integer's range that we can encode both
indexes. Since the integer is displayed in decimal in case of errors, use a
power of 10 to pack the two indexes together.

Signed-off-by: Manuel Pégourié-Gonnard <4ba0d615aeeda88e422ca8fba28fe2938485facf@arm.com>

ARMmbed/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls