drm_hwcomposer: Make flattening thread-based instead of vsync-based

Using vsync means consume some CPU time every frame for
IRQ -> Kernel_Thread -> UserSpace_listener thread transitions.

Framework tries to reduce vsync usage to the minimum, by using timelines
instead.

New flattening controller thread wakes-up only once per second.

This commit also removes flattening info from dumpsys. Practice shows
that it is almost useless. Instead debugging can be done using ALOGV
dumps.

Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>
diff --git a/meson.build b/meson.build
index 4328a1e..c2e5fb6 100644
--- a/meson.build
+++ b/meson.build
@@ -11,6 +11,7 @@
 
 src_common = files(
     'compositor/DrmKmsPlan.cpp',
+    'compositor/FlatteningController.cpp',
     'backend/BackendManager.cpp',
     'backend/Backend.cpp',
     'backend/BackendClient.cpp',