cpufreq: Kill userspace CPU boosting entirely

Kernel-based CPU boosting is used now, so stop userspace from messing with
it by turning scaling_min_freq into a no-op. Note that this is done instead
of making scaling_min_freq read-only so that userspace doesn't spit out
error messages when it can't do its boosting.

Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Signed-off-by: Danny Lin <danny@kdrag0n.dev>