drm/msm: UAPI error reporting

Debugging incorrect UAPI usage tends to be a bit painful, so add a
helper macro to make it easier to add debug logging which can be enabled
at runtime via drm.debug.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/630578/