Add extra clamp testing

Extend the QAI8 testing suite by iterating over clamp rates that will
clamp output range to no clamping, clamp 10% of range, and clamp 50% of
range

Signed-off-by: Emil Ohlsson <emil.ohlsson@arm.com>

Reviewed-by: Emil Ohlsson <emil.ohlsson@arm.com>
Approved-by: Felix Johnny Thomasmathibalan <felixjohnny.thomasmathibalan@arm.com>