1) timeout is unsigned, and clients tend to pass large unsigned values
   (like -1) to mean "wait as long as possible". Casting to signed at
   the start of the math meant that everything was negative, so we would
   never actually wait for fences to be signalled.

2) When going from nanoseconds to seconds, we should divide by 10^9, not
   multiply by 10^6.

3) Even with all of this, it's possible for a sufficiently large counter
   frequency to still cause overflow, so detect that case and clamp.

Change-Id: I9e728aac72d8dc0b15582732b6fd4d87c90bd140
Reviewed-on: https://chromium-review.googlesource.com/707202Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>