[WATCHDOG] w83697hf/hg WDT driver - patch 13

This is patch 13 in the series of patches that converts
Marcus Junker's w83697hf watchdog driver to Samuel Tardieau's
w83697hf/hg watchdog driver.

This patch contains following changes:
 - Remove wdt_ctrl (it has been replaced with the
   w83697hf_write_timeout() function) and redo/clean-up
   the start/stop/ping code.
 - Make sure that the watchdog is enabled or disabled
   When starting or stoping the device (with a call
   to w83697hf_set_reg(0x30, ?); ).

Signed-off-by: Samuel Tardieu <sam@rfc1149.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>