Add AES-CBF8 cypher to crypto module

This adds the aes_cfb8 cypher type (and associated tests and
documentation) to the crypto module.
Fix bug in SRP implementation

SRP didn't work with smaller primes as user secret was improperly
computed.

Formula is: (B - (k * g^x)) ^ (a + (u * x)) % N

Previously, the code computed a + (u * x) % N instead of a + (u * x).
a typically is a 256 bits random number (RFC 5054 says it should be at
least 256 bits), u and x are SHA1 signatures (160 bits). So a + (u * x)
can differ from a + (u * x) % N for N primes smaller than 320 bits.
crypto: Fix memory leak in hmac stream functions

The context was never deallocated.
crypto: Fix memory leak in some error cases

sign(dss,) and compute_key(dh,)
Merge branch 'pguyot/fix_srp' into maint

* pguyot/fix_srp:
  Fix bug in SRP implementation
crypto: Fix crypto for debug and valgrind

without relying on opt-version has been built.

Removed ASSERT to make crypto_callback.debug.so work without
dynamic linking to libcrypto.so.
crypto: Fix memory leak of EC "keys" and "points"
Merge branch 'sverk/crypto-ec-mem-leak/OTP-11999' into maint

* sverk/crypto-ec-mem-leak/OTP-11999:
  crypto: Fix memory leak of EC "keys" and "points"
  crypto: Fix crypto for debug and valgrind
Prepare release