hwc: Check for correct screen state before enabling vsync

Sometimes vsync would not be disabled before the display is
blanked.
This was due to the vsync disable ioctl being kicked off in a
thread different from the event control which surfaceflinger
called. So, while the calls from surfaceflinger are in order, the
order of execution wasn't always the same. Hence, making sure
ioctls are called in the same context to ensure order.

Also
- Make blanking/unblanking logs show the operation as a string.
- Add a debug property to dump vsync timestamps (needs framework
reboot)
- Remove a log which showed delay in reading vsync. This log was
unreliable when vsync is disabled and we're still reading from
the sysfs node.

Change-Id: Ibec04e9ffebd0ac6e1d32b7031e3668abd9390ff
CRs-fixed: 443113

Conflicts:
	libhwcomposer/hwc_utils.h
hwc: Check vsync state before sending it up

The vsync enable ioctl is called in  a separate thread in a
recent change
Hence it was now possible that vsync could be disabled but
SurfaceFlinger still received a vsync. With this check we make
sure that doesn't happen.

Change-Id: I459c0b98ab9ce972d86a361c5ecdfe0c1a2d0e74
Merge "hwc: Check for correct screen state before enabling vsync"
Merge "hwc: Check vsync state before sending it up"
Merge commit 'AU_LINUX_ANDROID_JB_1.9.6.04.03.00.143.023' into cm-10.2