hpwdt: Fix kdump issue in hpwdt

kdump can be interrupted by watchdog timer when the timer is left
activated on the crash kernel. Changed the hpwdt driver to disable
watchdog timer at boot-time. This assures that watchdog timer is
disabled until /dev/watchdog is opened, and prevents watchdog timer
to be left running on the crash kernel.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Tested-by: Lisa Mitchell <lisa.mitchell@hp.com>
Signed-off-by: Thomas Mingarelli <Thomas.Mingarelli@hp.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Cc: stable <stable@vger.kernel.org>