CONFIG_CRYPTO_MD5_OCTEON is not available for the selected architecture x86.
Result is shown for architecture mips

Digests: MD5 (OCTEON)

modulename: octeon-md5.ko

configname: CONFIG_CRYPTO_MD5_OCTEON

Linux Kernel Configuration
└─>Accelerated Cryptographic Algorithms for CPU (mips)
└─>Digests: MD5 (OCTEON)
In linux kernel since version 3.10 (release Date: 2013-06-30)
MD5 message digest algorithm (RFC1321)

Architecture: mips OCTEON using crypto instructions, when available
source code:
arch/mips/cavium-octeon/crypto/octeon-md5.c