libvpx

Change to allow less rectangular partion check

For CpuUsed 1 & 2, this commit allow to skip retangular partition check
when NONE is better than SPLIT. It also changed to allow such logic
on alt ref frame coding rather than use square partition all them. The
change has gain compressio about .3% on yt and ythd for both 1&2, It
helped .6% compression on cif and stdhd for both CpuUsed 1&2.

Change-Id: I814b653baf89f59acd20e042629a12938a1bd4e5