cmake/openimageio - partially reverting #60692

We now have openimageio building when cycles builds or when it's
manually set to build.

(I reverted the _IMAGE_ in the define name because I think the closer
the cmake flags match the defines in the software the better, and there
is no reason to rename all the existent WITH_OPENIMAGEIO references in
CMakeLists.txt - which would be the alternative)

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk@60718 954f8c5b-7b00-dc11-b283-0030488c597c