These are as similar to dscal_microk_skylakex-2.c as possible
for consistency.

Note that before this change SKYLAKEX+ uses generic C functions for
cscal/zscal via commit 2271c350 from #2610 (which is masked by
commit 086d87a30). However now #3799 disables FMAs (in turn enabled
by `-march=skylake-avx512`) in the plain C code which fixes excessive
LAPACK test failures more nicely.

If e.g. -march=haswell is set in CFLAGS, GCC generates FMAs by default, which
is inconsistent with the microkernels, none of which use FMAs. These
inconsistencies cause a few failures in the LAPACK testcases, where
eigenvalue results with/without eigenvectors are compared.

Moreover using FMAs for multiplication of complex numbers can give surprising
results, see 22aa81f for more information.

This uses the same syntax as used in 22aa81f for zarch (s390x).

Enable new build target platform -- COOPERLAKE. This target platform
supports all the SKYLAKEX supported ISAs + avx512bf16. So all the
SKYLAKEX specific kernels/drivers and related code are now extended
to be also active on COOPERLAKE. Besides, new BF16 related kernels
are active under this target.

This patch adds the basic infrastructure for adding the SkylakeX (Intel Skylake server)
target. The SkylakeX target will use the AVX512 (AVX512VL level) instruction set,
which brings 2 basic things:
1) 512 bit wide SIMD (2x width of AVX2)
2) 32 SIMD registers (2x the number on AVX2)

This initial patch only contains a trivial transofrmation of the Haswell SGEMM kernel
to AVX512VL; more will follow later but this patch aims to get the infrastructure
in place for this "later".

Full performance tuning has not been done yet; with more registers and wider SIMD
it's in theory possible to retune the kernels but even without that there's an
interesting enough performance increase (30-40% range) with just this change.