stm32f: Support hard reset
stm32f: Support hard reset

Now that we have hibernate ability, we can use this to perform a hard
reset.

BUG=chrome-os-partner:11579
TEST=Build success and working on 'snow':
       'reboot' and see reset cause is 'reset-pin soft'.
       'reboot hard' and see reset cause is 'hard'.
     Build success on 'daisy'.

Change-Id: I18132eee2f0d574d7d1674f7be25249dbe19749d
Signed-off-by: Vic Yang <5fd92abeee651458f98e2856f4f200ee971cee4d@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/27930
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

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