PM: runtime: Update kerneldoc return codes

APIs based on __pm_runtime_idle() (pm_runtime_idle(), pm_request_idle())
do not return 1 when already suspended. They return -EAGAIN. This is
already covered in the docs, so the entry for "1" is redundant and
conflicting.

(pm_runtime_put() and pm_runtime_put_sync() were previously incorrect,
but that's fixed in "PM: runtime: pm_runtime_put{,_sync}() returns 1
when already suspended", to ensure consistency with APIs like
pm_runtime_put_autosuspend().)

RPM_GET_PUT APIs based on __pm_runtime_suspend() do return 1 when
already suspended, but the language is a little unclear -- it's not
really an "error", so it seems better to list as a clarification before
the 0/success case. Additionally, they only actually return 1 when the
refcount makes it to 0; if the usage counter is still non-zero, we
return 0.

pm_runtime_put(), etc., also don't appear at first like they can ever
see "-EAGAIN: Runtime PM usage_count non-zero", because in non-racy
conditions, pm_runtime_put() would drop its reference count, see it's
non-zero, and return early (in __pm_runtime_idle()). However, it's
possible to race with another actor that increments the usage_count
afterward, since rpm_idle() is protected by a separate lock; in such a
case, we may see -EAGAIN.

Because this case is only seen in the presence of concurrent actors, it
makes sense to clarify that this is when "usage_count **became**
non-zero", by way of some racing actor.

Lastly, pm_runtime_put_sync_suspend() duplicated some -EAGAIN language.
Fix that.

Fixes: 271ff96d6066 ("PM: runtime: Document return values of suspend-related API functions")
Link: https://lore.kernel.org/linux-pm/aJ5pkEJuixTaybV4@google.com/
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: 6.17+ <stable@vger.kernel.org> # 6.17+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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