video: tegra: host: support in-kernel sync fence creation

Modify nvhost_sync_create_fence() to return sync_fence objects; move fd
handling + arg demarshalling into nvhost_ioctl_ctrl_sync_fence_create()

Change-Id: I548c189f982b31e506e4685b327556a7b7a91535
Signed-off-by: Greg Hackmann <ghackmann@google.com>

Conflicts:
	drivers/video/tegra/host/host1x/host1x.c
	drivers/video/tegra/host/nvhost_sync.c
	drivers/video/tegra/host/nvhost_sync.h

	modified:   drivers/video/tegra/host/host1x/host1x.c
	new file:   drivers/video/tegra/host/nvhost_sync.c
	new file:   drivers/video/tegra/host/nvhost_sync.h