IVGCVSW-2049 Create the CL Mean Float workload
IVGCVSW-2049 Create the CL Mean Float workload

 * Refactored HalPolicy::ConvertMean
 * Added sanity checks when parsing the Mean operands

Change-Id: Iea19556adb957b200e7fd01022a87230aaaf7157

ARM-software/android-nn-driver,ARM-software/android-nn-driver