Improve FIPS RSA keygen performance.

Reduce the Miller Rabin counts to the values specified by FIPS 186-5.
The old code was using a fixed value of 64.

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/19579)

(cherry picked from commit d2f6e66d)