tools/power/cpupower: Read energy_perf_bias from sysfs

... instead of poking at the MSR. For that, move the accessor functions
to misc.c and add a sysfs-writing function too.

There should be no functional changes resulting from this.

Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Cc: Thomas Renninger <trenn@suse.com>
Link: https://lkml.kernel.org/r/20201029190259.3476-2-bp@alien8.de