x86: intel_epb: Do not build when CONFIG_PM is unset

x86: intel_epb: Do not build when CONFIG_PM is unset

Commit 9ed0985332a6 ("x86: intel_epb: Take CONFIG_PM into account")
prevented the majority of the Performance and Energy Bias Hint (EPB)
handling code from being built when CONFIG_PM is unset to fix a
regression introduced by commit b9c273babce7 ("PM / arch: x86:
MSR_IA32_ENERGY_PERF_BIAS sysfs interface").

In hindsight, however, it would be better to skip all of the EPB
handling code for CONFIG_PM unset as there really is no reason for
it to be there in that case.  Namely, if the EPB is not touched
by the kernel at all with CONFIG_PM unset, there is no need to
worry about modifying the EPB inadvertently on CPU online and since
the system will not suspend or hibernate then, there is no need to
worry about possible modifications of the EPB by the platform
firmware during system-wide PM transitions.

For this reason, revert the changes made by commit 9ed0985332a6
and only allow intel_epb.o to be built when CONFIG_PM is set.

Note that this changes the behavior of the kernels built with
CONFIG_PM unset as they will not modify the EPB on boot if it is
zero initially any more, so it is not a fix strictly speaking, but
users building their kernels with CONFIG_PM unset really should not
expect them to take energy efficiency into account.  Moreover, if
CONFIG_PM is unset for performance reasons, leaving EPB as set
initially by the platform firmware will actually be consistent
with the user's expectations.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Ingo Molnar <mingo@kernel.org>