ANDROID: goldfish: Add goldfish sync driver

This is kernel driver for controlling the Goldfish sync
device on the host. It is used to maintain ordering
in critical OpenGL state changes while using
GPU emulation.

The guest open()'s the Goldfish sync device to create
a context for possibly maintaining sync timeline and fences.
There is a 1:1 correspondence between such sync contexts
and OpenGL contexts in the guest that need synchronization
(which in turn, is anything involving swapping buffers,
SurfaceFlinger, or Hardware Composer).

The ioctl QUEUE_WORK takes a handle to a sync object
and attempts to tell the host GPU to wait on the sync object
and deal with signaling it. It possibly outputs
a fence FD on which the Android systems that use them
(GLConsumer, SurfaceFlinger, anything employing
EGL_ANDROID_native_fence_sync) can use to wait.

Design decisions and work log:

- New approach is to have the guest issue ioctls that
  trigger host wait, and then host increments timeline.
- We need the host's sync object handle and sync thread handle
  as the necessary information for that.
- ioctl() from guest can work simultaneously with the
  interrupt handling for commands from host.
- optimization: don't write back on timeline inc
- Change spin lock design to be much more lightweight;
  do not call sw_sync functions or loop too long
  anywhere.
- Send read/write commands in batches to minimize guest/host
  transitions.
- robustness: BUG if we will overrun the cmd buffer.
- robustness: return fd -1 if we cannot get an unused fd.
- correctness: remove global mutex
- cleanup pass done, incl. but not limited to:
    - removal of clear_upto and
    - switching to devm_***

This is part of a sequential, multi-CL change:

external/qemu:

https://android-review.googlesource.com/239442 <- host-side device's
host interface

https://android-review.googlesource.com/221593
https://android-review.googlesource.com/248563
https://android-review.googlesource.com/248564
https://android-review.googlesource.com/223032

external/qemu-android:

https://android-review.googlesource.com/238790 <- host-side device
implementation

kernel/goldfish:

https://android-review.googlesource.com/232631 <- needed
https://android-review.googlesource.com/238399 <- this CL

Also squash following bug fixes from android-goldfish-3.18 branch.

b44d486 goldfish_sync: provide a signal to detect reboot
ad1f597 goldfish_sync: fix stalls by avoiding early kfree()
de208e8 [goldfish-sync] Fix possible race between kernel and user space

Change-Id: I22f8a0e824717a7e751b1b0e1b461455501502b6

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