drm/msm: fix locking inconsistencies in gpu->destroy()

In error paths, this was being called without struct_mutex held.
Leading to panics like:

  msm 1a00000.qcom,mdss_mdp: No memory protection without IOMMU
  Kernel panic - not syncing: BUG!
  CPU: 0 PID: 1409 Comm: cat Not tainted 4.0.0-dirty #4
  Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC (DT)
  Call trace:
  [<ffffffc000089c78>] dump_backtrace+0x0/0x118
  [<ffffffc000089da0>] show_stack+0x10/0x20
  [<ffffffc0006686d4>] dump_stack+0x84/0xc4
  [<ffffffc0006678b4>] panic+0xd0/0x210
  [<ffffffc0003e1ce4>] drm_gem_object_free+0x5c/0x60
  [<ffffffc000402870>] adreno_gpu_cleanup+0x60/0x80
  [<ffffffc0004035a0>] a3xx_destroy+0x20/0x70
  [<ffffffc0004036f4>] a3xx_gpu_init+0x84/0x108
  [<ffffffc0004018b8>] adreno_load_gpu+0x58/0x190
  [<ffffffc000419dac>] msm_open+0x74/0x88
  [<ffffffc0003e0a48>] drm_open+0x168/0x400
  [<ffffffc0003e7210>] drm_stub_open+0xa8/0x118
  [<ffffffc0001a0e84>] chrdev_open+0x94/0x198
  [<ffffffc000199f88>] do_dentry_open+0x208/0x310
  [<ffffffc00019a4c4>] vfs_open+0x44/0x50
  [<ffffffc0001aa26c>] do_last.isra.14+0x2c4/0xc10
  [<ffffffc0001aac38>] path_openat+0x80/0x5e8
  [<ffffffc0001ac354>] do_filp_open+0x2c/0x98
  [<ffffffc00019b60c>] do_sys_open+0x13c/0x228
  [<ffffffc00019b72c>] SyS_openat+0xc/0x18
  CPU1: stopping

But there isn't any particularly good reason to hold struct_mutex for
teardown, so just standardize on calling it without the mutex held and
use the _unlocked() versions for GEM obj unref'ing
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/adreno/adreno_gpu.c

@@ -384,7 +384,7 @@ void adreno_gpu_cleanup(struct adreno_gpu *gpu)
 	if (gpu->memptrs_bo) {
 		if (gpu->memptrs_iova)
 			msm_gem_put_iova(gpu->memptrs_bo, gpu->base.id);
-		drm_gem_object_unreference(gpu->memptrs_bo);
+		drm_gem_object_unreference_unlocked(gpu->memptrs_bo);
 	}
 	release_firmware(gpu->pm4);
 	release_firmware(gpu->pfp);

drivers/gpu/drm/msm/msm_drv.c

@@ -145,8 +145,8 @@ static int msm_unload(struct drm_device *dev)
 	if (gpu) {
 		mutex_lock(&dev->struct_mutex);
 		gpu->funcs->pm_suspend(gpu);
-		gpu->funcs->destroy(gpu);
 		mutex_unlock(&dev->struct_mutex);
+		gpu->funcs->destroy(gpu);
 	}
 
 	if (priv->vram.paddr) {

drivers/gpu/drm/msm/msm_ringbuffer.c

@@ -56,6 +56,6 @@ struct msm_ringbuffer *msm_ringbuffer_new(struct msm_gpu *gpu, int size)
 void msm_ringbuffer_destroy(struct msm_ringbuffer *ring)
 {
 	if (ring->bo)
-		drm_gem_object_unreference(ring->bo);
+		drm_gem_object_unreference_unlocked(ring->bo);
 	kfree(ring);
 }