PM: Move two sleep-related functions under CONFIG_PM_SLEEP

Since pm_runtime_force_resume() and pm_runtime_need_not_resume() are only
needed for handling system-wide PM transitions, there is no reason to
compile them in if CONFIG_PM_SLEEP is unset.

Accordingly, move them under CONFIG_PM_SLEEP and make the static
inline stub for pm_runtime_force_resume() return an error to indicate
that it should not be used outside CONFIG_PM_SLEEP.

Putting pm_runtime_force_resume() also allows subsequent changes to
be more straightforward because this function is going to access a
device PM flag that is only defined when CONFIG_PM_SLEEP is set.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://patch.msgid.link/3384523.aeNJFYEL58@rjwysocki.net