drivers/char/random: hackbench performance fix

Bugzilla: https://bugzilla.redhat.com/2109238

IBM has reported an up to 26% performance hit with hackbench due to some
random commits that were introduced in RHEL9 for the -rt kernel.

They provided a tested list of commits that resolve the problem.

Omitted-fix: 527a9867af29 ("random: do not split fast init input in add_hwgenerator_randomness()")
The split code is not present in RHEL9.

Signed-off-by: Prarit Bhargava prarit@redhat.com