GATHERV/SCATTERV should use uint32_t vectors as indices.

[edanor]

Current interface definition states, that the gather/scatter operations are using vectors of the same precision as the scalar type used. This is OK for 32b and 64b types, but might be troublesome for 8b and 16b scalars. Having only 8b indexing values might be too small to handle most of the problems.

The interface should be changed so that:

    UME_FUNC_ATTRIB DERIVED_VEC_TYPE & gather (SCALAR_TYPE const * baseAddr, DERIVED_UINT_VEC_TYPE const & indices) {

is replaced by something like:
UME_FUNC_ATTRIB DERIVED_VEC_TYPE & gather (SCALAR_TYPE const * baseAddr, SIMDVec<uint32_t, VEC_LEN> const & indices) {

This might require extending the traits to give back a uint32_t vector of the same length, or by extending the SIMDVecGatherScatterInterface with an additional template parameter. At the same time the code has to be update for all plugins.