The nvidia binary blob sometimes defers tx completion notification to the OS dependent layer.  Thus, the watchdog timer can go off when the tx engine is working fine but the OS dependent layer just hasn't been called to cleanup finished tx transactions.  To workaround this, when the watchdog fires, poke the binary blob to force it to flush any pending tx completions.  If this drops the pending tx count to zero then just return without logging a message or resetting the chip.
The nvidia binary blob sometimes defers tx completion notification to the
OS dependent layer.  Thus, the watchdog timer can go off when the tx
engine is working fine but the OS dependent layer just hasn't been called
to cleanup finished tx transactions.  To workaround this, when the watchdog
fires, poke the binary blob to force it to flush any pending tx
completions.  If this drops the pending tx count to zero then just return
without logging a message or resetting the chip.

This reportedly fixes the 'device timeout()' errors with at least several
NF4 nve(4) parts.

Submitted by:	Nathan Alexander Whitehorn <nathanw@uchicago.edu> (code)
Submitted by:	dg (inspiration for comment and explanation)
MFC after:	1 week

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