Scale the distortion mectric with tx size
Scale the distortion mectric with tx size

Properly scale the distortion metric according to the tranfer
function gain of the transform block size.

Change-Id: I8e3539d8936f5db78c1352f902f72ef19fc09ed8

webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx,webmproject/libvpx