platform/chrome: cros_ec: Expose suspend_timeout_ms in debugfs

In modern Chromebooks, the embedded controller has a mechanism where
it will watch a hardware-controlled line that toggles in suspend, and
wake the system up if an expected sleep transition didn't occur. This
can be very useful for detecting power management issues where the
system appears to suspend, but doesn't actually reach its lowest
expected power states.

Sometimes it's useful in debug and test scenarios to be able to control
the duration of that timeout, or even disable the EC timeout mechanism
altogether. Add a debugfs control to set the timeout to values other
than the EC-defined default, for more convenient debug and
development iteration.

Signed-off-by: Evan Green <evgreen@chromium.org>
Reviewed-by: Prashant Malani <pmalani@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Link: https://lore.kernel.org/r/20220822144026.v3.1.Idd188ff3f9caddebc17ac357a13005f93333c21f@changeid
[tzungbi: fix one nit in Documentation/ABI/testing/debugfs-cros-ec.]
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>

include/linux/platform_data/cros_ec_proto.h

@@ -169,6 +169,7 @@ struct cros_ec_device {
 	int event_size;
 	u32 host_event_wake_mask;
 	u32 last_resume_result;
+	u16 suspend_timeout_ms;
 	ktime_t last_event_time;
 	struct notifier_block notifier_ready;