CHROMIUM: watchdog: add WDIOC_GETBOOTSTATUS support to s3c2410_wdt

CHROMIUM: watchdog: add WDIOC_GETBOOTSTATUS support to s3c2410_wdt

Exynos5 can report the most recent "reset" (or boot) cause.  In particular,
WDIOC_GETBOOTSTATUS ioctl (to /dev/watchdog) can let users know if
the HW watchdog timed out and reset the machine.

BUG=chrome-os-partner:9403
TEST=manual

Change-Id: Iceb63d8404e25200846f75e6ce44da62749246dd
Signed-off-by: Grant Grundler <grundler@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/42759
Reviewed-by: Doug Anderson <dianders@chromium.org>