mrst_pmu: driver for Intel Moorestown Power Management Unit

The Moorestown (MRST) Power Management Unit (PMU) driver
directs the SOC power states in the "Langwell" south complex (SCU).

It hooks pci_platform_pm_ops[] and thus observes all PCI ".set_state"
requests.  For devices in the SC, the pmu driver translates those
PCI requests into the appropriate commands for the SCU.

The PMU driver helps implement S0i3, a deep system idle power idle state.
Entry into S0i3 is via cpuidle, just like regular processor c-states.
S0i3 depends on pre-conditions including uni-processor, graphics off,
and certain IO devices in the SC must be off.  If those pre-conditions
are met, then the PMU allows cpuidle to enter S0i3, otherwise such requests
are demoted, either to Atom C4 or Atom C6.

This driver is based on prototype work by Bruce Flemming,
Illyas Mansoor, Rajeev D. Muralidhar, Vishwesh M. Rudramuni,
Hari Seshadri and Sujith Thomas.  The current driver also
includes contributions from H. Peter Anvin, Arjan van de Ven,
Kristen Accardi, and Yong Wang.

Thanks for additional review feedback from Alan Cox and Randy Dunlap.

Acked-by: Alan Cox <alan@linux.intel.com>
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>