dmaengine: ioat: Support in-use unbind

Don't allocate memory using the devm infrastructure and instead call
kfree with the new dmaengine device_release call back. This ensures
the structures are available until the last reference is dropped.

We also need to ensure we call ioat_shutdown() in ioat_remove() so
that all the channels are quiesced and further transaction fails.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/20191216190120.21374-6-logang@deltatee.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>