It is reported that on some platforms, resume speed is not fast. The cause
is: in noirq stage, EC driver is working in polling mode, and each state
machine advancement requires a context switch.

The context switch is not necessary to the EC driver's polling mode. This
patch implements PM hooks to automatically switch the driver to/from the
busy polling mode to eliminate the overhead caused by the context switch.

This finally contributes to the tuning result: acpi_pm_finish() execution
time is improved from 192ms to 6ms.
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Reported-and-tested-by: Todd E Brandt <todd.e.brandt@linux.intel.com>
[ rjw: Subject ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>