Tweak allocation vars for XYZ space for more accurate GPU transform

Also extend 3DLUT edge size to 64 (1 meg of memory) to increase
transform accuracy as well.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56377 954f8c5b-7b00-dc11-b283-0030488c597c