CONFIG_CRYPTO_SALSA20_X86_64 is not available for thedefaultarchitecture x86.
Result is shown for architecture 64BIT
default or selected kernelversion does not have config value CONFIG_CRYPTO_SALSA20_X86_64.
Result is shown for kernelversion 6.5.1

Salsa20 stream cipher algorithm (x86_64)

modulename: salsa20-x86_64.ko

configname: CONFIG_CRYPTO_SALSA20_X86_64

Linux Kernel Configuration
└─>Cryptographic API
└─>Salsa20 stream cipher algorithm (x86_64)
In linux kernel since version 2.6.25 (release Date: 2008-04-16)  
Salsa20 stream cipher algorithm.

Salsa20 is a stream cipher submitted to eSTREAM, the ECRYPT
Stream Cipher Project. See <http://www.ecrypt.eu.org/stream/>

The Salsa20 stream cipher algorithm is designed by Daniel J.
Bernstein <djb@cr.yp.to>. See <http://cr.yp.to/snuffle.html>

source code:

depends
CONFIG_64BIT
CONFIG_CRYPTO
CONFIG_UML_X86 or CONFIG_X86