drm/panfrost: Improve error reporting in panfrost_gpu_power_on

It is useful to know which component cannot be powered on.

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200207052627.130118-4-drinkcat@chromium.org