Fix SHA256 usage on older CESA versions

Adding SHA256 support to Marvell crypto driver resulted in regression
for older SoC's, not capable of handling this mode in hardware.

Submitted by: Emeric Poupon <emeric.poupon@stormshield.eu>
Obtained from: Stormshield
Sponsored by: Stormshield
Reviewed by: zbb
Differential revision: https://reviews.freebsd.org/D9215