i965: Scale shader_time to compensate for resets.

i965: Scale shader_time to compensate for resets.

Some shaders experience resets more than others, which skews the numbers
reported.  Attempt to correct for this by linearly scaling according to
the number of resets that happen.

Note that will not be accurate if invocations of shaders have varying
times and longer invocations are more likely to reset.  However, this
should at least be better than the previous situation.