drm/panfrost: Add sanity checks to submit IOCTL

So userspace can get feedback on any error conditions, instead of going
ahead and things breaking later.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190424131355.62817-1-tomeu.vizoso@collabora.com