Add intelpmc(4), a driver for the power management controller found on

Add intelpmc(4), a driver for the power management controller found on
various Intel SoCs.  The driver takes care of calling the AML methods
needed to enter low power idle states during suspend-to-idle (S0i).
The driver also implements some debug code that prints the residency of
various power states in dmesg.  Based on some earlier code by jcs@

ok jcs@