This CL follows the original one"Sample selection in warped motion", and
aims to reduce the number of samples gathered. We only search 1 above row
and 1 left column instead of 1/2 bsize range in each direction. The gain
is a little less, but not much.

Borg test result:
             avg_psnr ovr_psnr ssim
cam_lowres:  -0.225   -0.228  -0.231
lowres:      -0.081   -0.075  -0.114

The changes are wrapped in WARPED_MOTION_SORT_SAMPLES macro.

Change-Id: Ifb499c80470b2ffe7a40f68fc401589faada7730