Adds the VPOPCNTDQ instruction set, providing packed population count for
double and quadword integers.
These are added via the `opcodesextra` mechanism #345, since they're missing
from the opcodes database. In this case the 512-bit non-AVX512VL forms are
added here as well as the opcodes database, but they're deduplicated later.
Contributed by @vsivsi. Extracted from #234 with simplifications for AVX-512
form expansion.
Co-authored-by: Vaughn Iverson <vsivsi@yahoo.com>
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