Fixed skippable evaluation in mode decision

Yunqing fixed an oddity in UVIntra skippable evaluation for stable
branch, which brought up the fact that the evaluation is broken.
The issue was that for MBs with 2nd order block, the eob for 1st
order blocks is set at 1. The previous evaluation did not take that
into account. This commit intend to fix the problem. The commit also
absorbed Yunqing's fix for UVIntra skippable evalution.

Test on hd showed some good gains in combination with LPF bias fix:
http://www.corp.google.com/~yaowu/no_crawl/LPFBias_FixSkip.html
(avg psnr: .34%, glb psnr: .32%, ssim: .22%)

Change-Id: I36af11c8ef7f643e8ff46da7bf3a167b437039d4