Propagate SWITCH_RATIO to DYNAMIC_ARCH builds

Previously dynamic builds were either using the default SWITCH_RATIO
or one from the higher level architecture; this patch ensures the
dynamic builds can use this parameter as well.

1. Use UZP instructions but not gather load and scatter store instructions to get lower latency.
    2. Padding k to a power of 4.

Add `OPENBLAS_DEFAULT_NUM_THREADS`

This allows Julia to set a default number of threads (usually `1`) to be
used when no other thread counts are specified [0], to short-circuit the
default OpenBLAS thread initialization routine that spins up a different
number of threads than Julia would otherwise choose.

The reason to add a new environment variable is that we want to be able
to configure OpenBLAS to avoid performing its initial memory
allocation/thread startup, as that can consume significant amounts of
memory, but we still want to be sensitive to legacy codebases that set
things like `OMP_NUM_THREADS` or `GOTOBLAS_NUM_THREADS`.  Creating a new
environment variable that is openblas-specific and is not already
publicly used to control the overall number of threads of programs like
Julia seems to be the best way forward.

[0] https://github.com/JuliaLang/julia/pull/46844

Make it work on general MIPS64 processors

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>

It is really dangerous to fallback to Loongson core on other
MIPS64 processors.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>

Some compilers (namely LLVM) are not happy with clobbering
registers in inline assembly.
Use $at as temporary register and explicitly use noat
hint.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>

Add env variable OMP_ADAPTIVE to control OMP threadpool behaviour

It's safer and easier than SIGILL.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>

LoongArch64: Add DYNAMIC_ARCH support

* fix detection of Neoverse V1 and user-enforced selection of N2

This fixes compilation in the following case:

$(MAKE) USE_OPENMP=1 USE_THREAD=1 NO_LAPACK=0 DYNAMIC_ARCH=1 \
DYNAMIC_LIST="HASWELL SKYLAKEX ATOM COOPERLAKE SAPPHIRERAPIDS ZEN"

Support Zhaoxin/Centaur kh40000 as ZEN

Signed-off-by: JonasZhou <JonasZhou@zhaoxin.com>

WIP casts and cleanups

OpenBLAS: aarch64: Add neoverse-v1/n2 architecture specifics

* Move accesses to the overflow flag into the scope of the blas lock