watchdog: Add WDIOC_GETTIMELEFT ioctl support to w83627 watchdog driver

Add WDIOC_GETTIMELEFT ioctl allowing you to check how much time is left
on the watchdog counter before a reset occurs.

Signed-off-by: Greg Lee <glee [at] swspec.com>
Signed-off-by: Padraig Brady <P@draigbrady.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Signed-off-by: Andrew Morton <akpm@google.com>