Check for WELS_CPU_NEON before calling DeblockingBSCalcEnc_neon

Checking HAVE_NEON is not enough; e.g. android devices with
armeabi-v7a are not required to have NEON, so every use of such
functions should be check WELS_CPU_NEON in the cpu features
as well.
Merge pull request #750 from mstorsjo/deblocking-neon-cpu-features

Check for WELS_CPU_NEON before calling DeblockingBSCalcEnc_neon