[CPUFREQ] xen: governor for Xen hypervisor frequency scaling.

[CPUFREQ] xen: governor for Xen hypervisor frequency scaling.

This CPU freq governor leaves the frequency decision to the Xen hypervisor.

To do that the driver parses the Power Management data and uploads said
information to the Xen hypervisor. Then the Xen hypervisor can select the
proper Cx and Pxx states for the initial domain and all other domains.

To upload the information, this CPU frequency driver reads Power Management (PM)
(_Pxx and _Cx) which are populated in the 'struct acpi_processor' structure.
It simply reads the contents of that structure and pass it up the Xen hypervisor.
For that to work we depend on the appropriate CPU frequency scaling driver
to do the heavy-lifting - so that the contents is correct.

The CPU frequency governor it has been loaded also sets up a timer
to check if the ACPI IDs count is different from the APIC ID count - which
can happen if the user choose to use dom0_max_vcpu argument. In such a case
a backup of the PM structure is used and uploaded to the hypervisor.

[v1-v2: Initial RFC implementations that were posted]
[v3: Changed the name to passthru suggested by Pasi Kärkkäinen <pasik@iki.fi>]
[v4: Added vCPU != pCPU support - aka dom0_max_vcpus support]
[v5: Cleaned up the driver, fix bug under Athlon XP]
[v6: Changed the driver to a CPU frequency governor]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Conflicts:

	drivers/xen/Kconfig
	drivers/xen/Makefile