Adaptive ARF factor decision

Adaptive ARF factor decision

Re-count the factors to decide bit boost factor for the
intermediate layer ARFs. Make the gfu_boost factor assigned to
each ARF adapt to its local factors.

This and the recursive change 5bfe9eb together improves the
multi-layer ARF compression performance:

          avg_psnr      ovr_psnr     ssim
lowres    -0.39%        -0.54%       -1.6%
midres    -0.98%        -1.26%       -2.3%
hdres     -0.95%        -1.13%       -2.3%

Change-Id: I5fec3ea75cae58825787dc88dadc7e8697a041ea