fsi: Coldfire coprocessor offload

This series implements support for offloading the FSI protocol bitbanging to the ColdFire secondary core of the Aspeed SoCs. The result increases FSI performance by a factor of 4, and on systems that don't support async FSI clock, provide much more regular and continuous clocking which helps reliability.

This series is much smaller than the previous submissions as I already merged all the "preparatory" work into the FSI tree. This is now strictly the coldfire support and is now only waiting for ack of the DT bindings (and whatever other review comments might come my way) before I put it into the FSI tree and sends it to Greg.

There are two dependencies to be able to build/use this. The above prep work:

https://git.kernel.org/pub/scm/linux/kernel/git/benh/linux-fsi.git/log/

And the Aspeed GPIO driver changes for handling with GPIO lines ownership and handshaking. The patches have been merged into the GPIO tree and a dedicated immutable topic branch and can be found here:

https://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-gpio.git/log/?h=ib-aspeed

Finally, the driver needs a machine specific firmware file. The firwmare is open source and available at:

https://github.com/ozbenh/cf-fsi

I will submit it to linux-firmware if there's enough popular demand ;-)

v2. Fix misuse of devm_kzalloc for objects containing a struct device
in fsi-master-gpio and fsi-master-ast-cf (similar fixes for the various FSI drivers will come later a part of rework to move away from misc devs).

v3. Sparse fix and updated DT bindings as per Rob's comments.