ACPI / LPSS: Consolidate runtime PM and system sleep handling

Move the LPSS-specific code from acpi_lpss_runtime_suspend()
and acpi_lpss_runtime_resume() into separate functions,
acpi_lpss_suspend() and acpi_lpss_resume(), respectively, and
make acpi_lpss_suspend_late() and acpi_lpss_resume_early() use
them too in order to unify the runtime PM and system sleep
handling in the LPSS driver.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>