drm/msm/gpu: Fix crash during system suspend after unbind

In adreno_unbind, we should clean up gpu device's drvdata to avoid
accessing a stale pointer during system suspend. Also, check for NULL
ptr in both system suspend/resume callbacks.

Signed-off-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/505075/
Link: https://lore.kernel.org/r/20220928124830.2.I5ee0ac073ccdeb81961e5ec0cce5f741a7207a71@changeid
Signed-off-by: Rob Clark <robdclark@chromium.org>