Add DYNAMIC_ARCH support for ARM64

Enable DYNAMIC_ARCH feature on ARM64. This patch uses the cpuid
feature in linux kernel to detect the core type at runtime
(https://www.kernel.org/doc/Documentation/arm64/cpu-feature-registers.txt).

If this feature is missing in kernel, then the user should use the
OPENBLAS_CORETYPE env variable to select the desired core type.

Remove the runtime setting of P, Q, R parameters for
targets ARMV8, THUNDERX2T99. Instead set them as constants
in param.h at compile time.

Remove XGENE1 target as the implementation for the
same is incomplete. Moreover whoever wishes to use
on XGENE1 can use the generic ARMV8 target as there
are no XGENE1 specific optimizations in OpenBLAS.

Delay _hemv threading in attempt to address #1820

Use ThunderX2 Neon Kernels for ARMV8 Target

Currently the generic ARMV8 target uses C implementations
for many routines. Replace these with the neon implementations
written for THUNDERX2T99 target which are upto 6x faster for
certain routines.

enable the SGEMM/SKX C based kernel

In QA the final bug was found so now the sklyakex sgemm C based kernel can
be activated....

Use KERNEL_DEFINITIONS rather than COMMON_OPTS to pass -march=skylake…

Add -march=skylake-avx512 to CFLAGS when the target is Skylake

Revert "Add -march=skylake-avx512 when required"

Should fix 1806 and #1801

Use avx512 workaround with msys2/mingw64 as well

Add a C+intrinsics version of the SGEMM/skylakex kernel

for most sizes this is 1.2x to 1.4x faster than the current code

Update common_mips64.h for the 1st loop of blas_memory_alloc

Improve CMake help output and add SYMBOLPREFIX and -SUFFIX options

Handle conflicting usage of ARCH in at least some BSD environments

Add optimized *copy versions for skylakex

fixes #1796

in case a conflicting setting of ARCH (for architecture) gets pulled in from the environment
(originally suggested by dloghin in #1753)

Add -march=skylake-avx512 when required

fixes #1797

very minor gains since it's not super hot code, but general principles

fix parallel build issues with APFS/HFS+/ext2/3 in netlib-lapack

the compare is more costly than the work

Add optimized n/t copy versions for skylakex; in the patch the
tcopy is also rewritten using intrinsics; the ncopy file
will be worked on in a future commit

merge develop

The problem is that OpenBLAS sets the LAPACKE_LIB and the TMGLIB to the
same object and uses the `ar` feature to update the archive file. If the
underlying filesystem does not have sub-second timestamp resolution and
the system is fast enough (or `ccache` is used), the timestamp of the
builds which should be added to the previously generated archive is the
same as the archive file itself and therefore `make` does not update the
archive.

Since OpenBLAS takes care to not run the different targets updating the
archive in parallel, the easiest solution is to declare the respective
targets `.PHONY`, forcing `make` to always update them.

fixes #1682

update travis alpine chroot with avx512 intrinsics headers

skylake dgemm: Add a 16x8 kernel