power: common interface for guest and host

power: common interface for guest and host

Moved the current librte_power implementation to rte_power_acpi_cpufreq, with
renaming of functions only.
Added rte_power_kvm_vm implementation to support Power Management from a VM.

librte_power now hides the implementation based on the environment used.
A new call rte_power_set_env() can explicidly set the environment, if not
called then auto-detection takes place.

rte_power_kvm_vm is subset of the librte_power APIs, the following is supported:
 rte_power_init(unsigned lcore_id)
 rte_power_exit(unsigned lcore_id)
 rte_power_freq_up(unsigned lcore_id)
 rte_power_freq_down(unsigned lcore_id)
 rte_power_freq_min(unsigned lcore_id)
 rte_power_freq_max(unsigned lcore_id)

The other unsupported APIs return -ENOTSUP

Signed-off-by: Alan Carew <alan.carew@intel.com>
Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>