Add intrinsics for LSX and LASX
This adds actual intrinsics of SIMD on loongarch64, with considerable performance improvements.
Benchmark on `Loongson-3A6000-HV Not Specified CPU @ 2.5GHz`
Baseline GCC 14 (debian trixie):
```
===========================
Total time (ms) : 17816
Nodes searched : 2336177
Nodes/second : 131128
```
With this PR:
GCC 16 (debian sid):
```
./stockfish compiler
Stockfish dev-20260516-52e8d9ef by the Stockfish developers (see AUTHORS file)
Compiled by : g++ (GNUC) 16.1.0 on Linux
Compilation architecture : loongarch64-lasx
Compilation settings : 64bit LASX LSX
Compiler __VERSION__ macro : 16.1.0
===========================
Total time (ms) : 3518
Nodes searched : 2336177
Nodes/second : 664063
```
```
./stockfish compiler
Stockfish dev-20260516-52e8d9ef by the Stockfish developers (see AUTHORS file)
Compiled by : g++ (GNUC) 16.1.0 on Linux
Compilation architecture : loongarch64-lsx
Compilation settings : 64bit LSX
Compiler __VERSION__ macro : 16.1.0
===========================
Total time (ms) : 4944
Nodes searched : 2336177
Nodes/second : 472527
```
clang 22 (debian sid):
```
./stockfish compiler
Stockfish dev-20260516-52e8d9ef by the Stockfish developers (see AUTHORS file)
Compiled by : clang++ 22.1.5 on Linux
Compilation architecture : loongarch64-lasx
Compilation settings : 64bit LASX LSX
Compiler __VERSION__ macro : Debian Clang 22.1.5 (1)
===========================
Total time (ms) : 3401
Nodes searched : 2336177
Nodes/second : 686908
```
```
./stockfish compiler
Stockfish dev-20260516-52e8d9ef by the Stockfish developers (see AUTHORS file)
Compiled by : clang++ 22.1.5 on Linux
Compilation architecture : loongarch64-lsx
Compilation settings : 64bit LSX
Compiler __VERSION__ macro : Debian Clang 22.1.5 (1)
===========================
Total time (ms) : 5501
Nodes searched : 2336177
Nodes/second : 424682
```
GCC 14 (debian trixie):
```
./stockfish compiler
Stockfish dev-20260516-52e8d9ef by the Stockfish developers (see AUTHORS file)
Compiled by : g++ (GNUC) 14.2.0 on Linux
Compilation architecture : loongarch64-lasx
Compilation settings : 64bit LASX LSX
Compiler __VERSION__ macro : 14.2.0
===========================
Total time (ms) : 3559
Nodes searched : 2336177
Nodes/second : 656413
```
```
./stockfish compiler
Stockfish dev-20260516-52e8d9ef by the Stockfish developers (see AUTHORS file)
Compiled by : g++ (GNUC) 14.2.0 on Linux
Compilation architecture : loongarch64-lsx
Compilation settings : 64bit LSX
Compiler __VERSION__ macro : 14.2.0
===========================
Total time (ms) : 5212
Nodes searched : 2336177
Nodes/second : 448230
```
clang 19 (debian trixie):
```
./stockfish compiler
Stockfish dev-20260516-52e8d9ef by the Stockfish developers (see AUTHORS file)
Compiled by : clang++ 19.1.7 on Linux
Compilation architecture : loongarch64-lasx
Compilation settings : 64bit LASX LSX
Compiler __VERSION__ macro : Debian Clang 19.1.7 (3+b1)
===========================
Total time (ms) : 4830
Nodes searched : 2336177
Nodes/second : 483680
```
```
./stockfish compiler
Stockfish dev-20260516-52e8d9ef by the Stockfish developers (see AUTHORS file)
Compiled by : clang++ 19.1.7 on Linux
Compilation architecture : loongarch64-lsx
Compilation settings : 64bit LSX
Compiler __VERSION__ macro : Debian Clang 19.1.7 (3+b1)
===========================
Total time (ms) : 5568
Nodes searched : 2336177
Nodes/second : 419572
```
closes https://github.com/official-stockfish/Stockfish/pull/6815
No functional change