[drbcc-wd] Watchdog write method with magic close

Sending random characters will be interpreted as a keepalive signal by the driver.
Sending a 'V' char will stop the watchdog driver.

Signed-off-by: Christina Quast <chrysh.ng+github@gmail.com>
[drbcc-wd]  Moved around defines

Signed-off-by: Christina Quast <chrysh.ng+github@gmail.com>
[drbcc-wd] Corrected pointers in get_user and put_user

Signed-off-by: Christina Quast <chrysh.ng+github@gmail.com>
[drbcc-wd] Timer for next kernel keepalive message

Signed-off-by: Christina Quast <chrysh.ng+github@gmail.com>