This change introduces the fsi device API: simple read, write and peek
accessors for the devices' address spaces.

Includes contributions from Christopher Bostic
<cbostic@linux.vnet.ibm.com> and Edward A. James <eajames@us.ibm.com>.
Signed-off-by: NEdward A. James <eajames@us.ibm.com>
Signed-off-by: NJeremy Kerr <jk@ozlabs.org>
Signed-off-by: NChristopher Bostic <cbostic@linux.vnet.ibm.com>
Signed-off-by: NJoel Stanley <joel@jms.id.au>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>