Adjust the qp threshold and consec_zeromv threshold for
limiting cyclic refresh. Also increase the refresh period
when the limit amount is significant, and some code-cleanup.

Small gain in PSNR/SSIM metrics: ~0.25/0.3 gain on RTC set, speed 7.

Change only affects non-screen content.

Change-Id: I1ced87a89a132684c071e722616e445b2d18236a