gpu: ipu-v3: image-convert: Prevent race between run and unprepare

Prevent possible race by parallel threads between ipu_image_convert_run()
and ipu_image_convert_unprepare(). This involves setting ctx->aborting
to true unconditionally so that no new job runs can be queued during
unprepare, and holding the ctx->aborting flag until the context is freed.

Note that the "normal" ipu_image_convert_abort() case (e.g. not during
context unprepare) should clear the ctx->aborting flag after aborting
any active run and clearing the context's pending queue. This is because
it should be possible to continue to use the conversion context and queue
more runs after an abort.

Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>