drm/vc4: Demote user-accessible DRM_ERROR paths to DRM_DEBUG.

drm/vc4: Demote user-accessible DRM_ERROR paths to DRM_DEBUG.

Userspace shouldn't be able to spam dmesg by passing bad arguments.
This has particularly become an issues since we started using a bad
argument to set_tiling to detect if set_tiling was supported.

Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: 83753117f1de ("drm/vc4: Add get/set tiling ioctls.")

[inki.dae: apply from rpi3-4.9.y]
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Change-Id: If0d72926b2a84d83eff06ae161502605df7e11e9