[bhnd] Initial power/clock management support.

[landonf]

Summary

Integrate initial PMU/PWRCTL driver support and supporting
bhnd(4) bus APIs:

• Add bus-level support for per-core clock and resource power requests.
• Add bhnd_pmu driver implementations for PMU and PWRCTL devices, derived from Broadcom's ISC-licensed HND code.

Depends on D7489
Depends on D7539

Test Plan

• Test for successful device attach on:
  • N16, N53, BCM43225, BCM4312 (PMU devices)
  • WGT634U (non-PMU, non-PWRCTL)
• Verify expected mem/cpu/bus frequency values under dev.bhnd_pmu sysctl

I could use a hand testing the PWRCTL code; I don't seem to have any
hardware that advertises PWRCTL support.

[landonf]

Drop unused static function declaration.

[landonf]

Rebase against HEAD.

[landonf]

• Resolve a minor conflict with the D7539 delta.

[adrian]

Does the code complain loudly if the hardware advertises PWRCTL support? That'd make it easier to evaluate.

[landonf]

In D7492#157065, @adrian wrote:

Does the code complain loudly if the hardware advertises PWRCTL support? That'd make it easier to evaluate.

Not currently (it'll use a device description of 'ChipCommon Power Control' that differentiates it from the PMU driver, but that's about it).

Something like "WARNING: Using untested PWRCTL support" ?

[adrian]

yes, something exactly like that. :)

[landonf]

Print a warning when using mostly-untested PWRCTL support.

[mizhka]

Looks fine. Let's land it :)