Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Introduce a new method, cpufreq_drv_type(), that returns the type of the
driver. This used to be handled by cpufreq_drv_settings() but it's
useful to get the type/flags separately from getting the settings.
(For example, you don't have to pass an array of cf_setting just to find
the driver type.)

Use this new method in our in-tree drivers to detect reliably if acpi_perf
is present and owns the hardware. This simplifies logic in drivers as well
as fixing a bug introduced in my last commit where too many drivers attached.

Add an interface for cpufreq. The kernel interface lets other drivers
select the CPU frequency level (say for cooling). The driver interface
allows hardware drivers to announce themselves as capable of adjusting
an individual frequency setting.