Start the dream manager even if dreams are not supported.

The dreams manager also manages dozing.  It has a minimal footprint
so there is no real reason to disable the component (it just makes
debugging more difficult).

Improved the documentation of the config_dreamsSupported resource
to clarify exactly what it controls.

Bug: 12494706
Change-Id: I78244846f7c1ddfd11bc1605af59b0db91337971

services/java/com/android/server/SystemServer.java

@@ -857,9 +857,8 @@ public final class SystemServer {
                 }
             }
 
-            if (!disableNonCoreServices
-                    && context.getResources().getBoolean(R.bool.config_dreamsSupported)) {
-                // Dreams (interactive idle-time views, a/k/a screen savers)
+            if (!disableNonCoreServices) {
+                // Dreams (interactive idle-time views, a/k/a screen savers, and doze mode)
                 mSystemServiceManager.startService(DreamManagerService.class);
             }