AVX2: make use of packed move (&extend)
AVX2: make use of packed move (&extend)

AVX2 has the _mm256_cvtep[iu]16_epi32 intrinsic to implement this
conversion.

Signed-off-by: Matthias Kretz <372ea4eca737a13cd010ee806d4ce7b98ee71550@kde.org>

VcDevel/Vc,chr-engwer/Vc,chr-engwer/Vc,VcDevel/Vc,chr-engwer/Vc,VcDevel/Vc,VcDevel/Vc