watchdog: ziirave_wdt: Add support to upload the firmware.

This patch adds and entry to the sysfs to start firmware upload process
on the specified device with the requested firmware.

The uploading of the firmware needs only to happen once per firmware
upgrade, as the firmware is stored in persistent storage. If the
firmware upload or the firmware verification fails then we print and
error message and exit.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>