arm: imx: Change imx6 target_residency to reduce latency

*FIXME* This is a workaround not a solution

The having a proper target_residency set causes excessive
latencies on the iMX6 SOC's.  I have experienced this as have
I read reports and seen patches by the Boundary team. Rather
than just disable cpu_idle all together I have tested and found
setting a 10ms target_residency solves the latency problem.