Make direct calls to Neon variance paths in Neon subpel variance

Now that we have Neon DotProd paths for subpel variance as well as
variance, we no longer need to have an indirect call to the variance
function in Armv8.0 Neon subpel variance paths. Make a direct call to
the Neon variance path in these Neon subpel functions.

This is a port from SVT-AV1:
https://gitlab.com/AOMediaCodec/SVT-AV1/-/merge_requests/2608

Originally authored by: Jonathan Wright <[email protected]>

Change-Id: If94c9af098356ec857255496a435b7a4cbb3c522
1 file changed