The following functionalities are supported:
 - write, read from volatile memory

Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/22060b.pdfSigned-off-by: NSlawomir Stepien <sst@poczta.fm>
Reviewed-by: NJoachim Eastwood <manabian@gmail.com>
Signed-off-by: NJonathan Cameron <jic23@kernel.org>