ipmi: Add a way to tune some timeouts

By default the retry timeout is 1 second.  Allow that to be modified,
primarily for slow operations, like firmware writes.

Also, the timeout was driven by a 1 second timer, so 1 second really
meant between 0 and 1 second.  Set the default to 2 seconds so it
means between 1 and 2 seconds.

Also allow the time the interface automatically stays in mainenance
mode to be modified from it's default 30 seconds.

Also consolidate some of the timeout and retry setup.

Signed-off-by: Corey Minyard <cminyard@mvista.com>

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