Add an engine driver to expose a "hub" FSI master - which has a set of
control registers in the engine address space, and uses a chunk of the
slave address space for actual FSI communication.

Additional changes from Jeremy Kerr .

Signed-off-by: Christopher Bostic
Signed-off-by: Jeremy Kerr
Signed-off-by: Joel Stanley
Signed-off-by: Greg Kroah-Hartman