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

Depends on !222 (merged) !221 (merged)

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.