FIX: [amc] add omx.exynos to white list

Ref: http://forum.xbmc.org/showthread.php?tid=187974&pid=1650396#pid1650396

Apparently, omx.exynos is lying on stride/slice, but works ok in Surface mode.

@davilla I know you had issues on Odroid / Exynos with Surface mode, but apparently they fixed it, at least on the Samsung tablets. Too bad we have no way (that I know) to check the version of an omx component... 
Probably an exynos4 vs. exynos5 difference, too...