Add force_suspend function

This CL implements a simple force_suspend().  This function takes a
timeoutMs argument that is currently ignored.  It also uses a two-stage
init process that spawns the suspend_thread when autosuspend is in use.

Follow-up CLs will:
- Implement file locking to prevent multiple libsuspend instances from
starting multiple suspend threads in the system.
- Fully implement timout for force_suspend.
- Integrate force_suspend with suspend_thred.

Bug: 70669809
Test:  autosuspend still works
Change-Id: I6b2c72d0c61d1bec6db0f0b28481ffe0e20ec615
diff --git a/libsuspend/autosuspend_ops.h b/libsuspend/autosuspend_ops.h
index 357b828..b0024c8 100644
--- a/libsuspend/autosuspend_ops.h
+++ b/libsuspend/autosuspend_ops.h
@@ -20,6 +20,7 @@
 struct autosuspend_ops {
     int (*enable)(void);
     int (*disable)(void);
+    int (*force_suspend)(int timeout_ms);
     void (*set_wakeup_callback)(void (*func)(bool success));
 };