mec1322: Check/save reset cause
mec1322: Check/save reset cause

So far we can only reliably sense a watchdog reset, but this
saving/checking reset cause will at least make 'ap-off' flag work.

BUG=chrome-os-partner:24107
TEST='waitms 2000' and see reset cause = 'watchdog'
TEST='reboot ap-off' and see reset cause includes 'ap-off'
TEST='reboot preserve' and see previous reset cause is preserved.
BRANCH=None

Change-Id: Id47a72d615489c9d9cd0b8761cfa699f08c724df
Signed-off-by: Vic (Chun-Ju) Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/178277
Reviewed-by: Vincent Palatin <70a9964ec8fd10b0b08fcc8623c2add25ddf99ac@chromium.org>

eatbyte/chromium-ec,alterapraxisptyltd/chromium-ec,fourier49/BIZ_EC,mtk09422/chromiumos-platform-ec,longsleep/ec,coreboot/chrome-ec,gelraen/cros-ec,mtk09422/chromiumos-platform-ec,thehobn/ec,longsleep/ec,gelraen/cros-ec,coreboot/chrome-ec,coreboot/chrome-ec,alterapraxisptyltd/chromium-ec,mtk09422/chromiumos-platform-ec,eatbyte/chromium-ec,coreboot/chrome-ec,akappy7/ChromeOS_EC_LED_Diagnostics,thehobn/ec,alterapraxisptyltd/chromium-ec,alterapraxisptyltd/chromium-ec,longsleep/ec,thehobn/ec,fourier49/BZ_DEV_EC,md5555/ec,fourier49/BIZ_EC,akappy7/ChromeOS_EC_LED_Diagnostics,mtk09422/chromiumos-platform-ec,fourier49/BZ_DEV_EC,fourier49/BIZ_EC,akappy7/ChromeOS_EC_LED_Diagnostics,coreboot/chrome-ec,fourier49/BZ_DEV_EC,eatbyte/chromium-ec,longsleep/ec,md5555/ec,thehobn/ec,akappy7/ChromeOS_EC_LED_Diagnostics,gelraen/cros-ec,fourier49/BIZ_EC,gelraen/cros-ec,md5555/ec,akappy7/ChromeOS_EC_LED_Diagnostics,eatbyte/chromium-ec,md5555/ec,fourier49/BZ_DEV_EC,coreboot/chrome-ec