ACPI / PNP: Use ACPI_COMPANION() instead of ACPI_HANDLE()

The ACPI_HANDLE() macro evaluates ACPI_COMPANION() internally to
return the handle of the device's ACPI companion, so it is much
more straightforward and efficient to use ACPI_COMPANION()
directly to obtain the device's ACPI companion object instead of
using ACPI_HANDLE() and acpi_bus_get_device() on the returned
handle for the same thing.

Do that in several places in the ACPI PNP core code.

Also use acpi_device_set_power() and acpi_device_power_manageable()
instead of acpi_bus_set_power() and acpi_bus_power_manageable(),
respectively, because the former two are more efficient if the
ACPI device object is already available.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>