Various IPMI watchdog timer improvements

o Make hw.ipmi.on a tuneable
o Changes to keep shutdown from hanging indefinitately after the wd

would normally have been disabled.

o Add support for setting pretimeout (which fires an interrupt

some time before the actual watchdog expires)

o Allow refinement of the actions to take when the watchdog expires
o Allow special startup timeout to keep us from hanging in boot

before watchdogd is started, but after we've loaded the kernel.

Obtained From: Netflix OCA Firmware