dt-bindings: fsi: Add specification for FSI busses

This change introduces a proposed layout for describing FSI busses in
the device tree. While the bus is probe-able, we'd still like a method
of describing subordinate (eg i2c) busses that are behind FSI devices.

The FSI core will be responsible for matching probed slaves & engines to
their device tree nodes, so the FSI device drivers' probe() functions
will be passed a struct device with the appropriate of_node populated
where a matching DT node is found.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Acked-by: Joel Stanley <joel@jms.id.au>
Acked-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Acked-by: Eddie James <eajames@linux.vnet.ibm.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>