drm/msm: Fix double pm_runtime_disable() call

Following commit 17e822f7 ("drm/msm: fix unbalanced
pm_runtime_enable in adreno_gpu_{init, cleanup}"), any call to
adreno_unbind() will disable runtime PM twice, as indicated by the call
trees below:

  adreno_unbind()
   -> pm_runtime_force_suspend()
   -> pm_runtime_disable()

  adreno_unbind()
   -> gpu->funcs->destroy() [= aNxx_destroy()]
   -> adreno_gpu_cleanup()
   -> pm_runtime_disable()

Note that pm_runtime_force_suspend() is called right before
gpu->funcs->destroy() and both functions are called unconditionally.

With recent addition of the eDP AUX bus code, this problem manifests
itself when the eDP panel cannot be found yet and probing is deferred.
On the first probe attempt, we disable runtime PM twice as described
above. This then causes any later probe attempt to fail with

  [drm:adreno_load_gpu [msm]] *ERROR* Couldn't power up the GPU: -13

preventing the driver from loading.

As there seem to be scenarios where the aNxx_destroy() functions are not
called from adreno_unbind(), simply removing pm_runtime_disable() from
inside adreno_unbind() does not seem to be the proper fix. This is what
commit 17e822f7 ("drm/msm: fix unbalanced pm_runtime_enable in
adreno_gpu_{init, cleanup}") intended to fix. Therefore, instead check
whether runtime PM is still enabled, and only disable it in that case.

Fixes: 17e822f7

 ("drm/msm: fix unbalanced pm_runtime_enable in adreno_gpu_{init, cleanup}")
Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Tested-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Link: https://lore.kernel.org/r/20220606211305.189585-1-luzmaximilian@gmail.com
Signed-off-by: Rob Clark <robdclark@chromium.org>