smaccm-commsec: refactor Config datatypes
smaccm-commsec: rename success error code
smaccm-commsec: changes for Config refactor, implement decode properly
smaccm-commsec: test tries to encode, then decode, compare results

test fails in commsec_decode_run with error `fail_gcm` - it looks like
for some reason the counters in encode and decode match up for their
first 12 most significant bytes but the last 4 are different for some reason.

i'm going to see if Tom knows what's going on.