Add Loongson Advanced SIMD Extension support: -DCPU_BASELINE=LASX

* Add Loongson Advanced SIMD Extension support: -DCPU_BASELINE=LASX
* Add resize.lasx.cpp for Loongson SIMD acceleration
* Add imgwarp.lasx.cpp for Loongson SIMD acceleration
* Add LASX acceleration support for dnn/conv
* Add CV_PAUSE(v) for Loongarch
* Set LASX by default on Loongarch64
* LoongArch: tune test threshold for Core/HAL.mat_decomp/15

Co-authored-by: shengwenxue <shengwenxue@loongson.cn>

cmake/checks/cpu_lasx.cpp

@@ -0,0 +1,23 @@
+#include <stdio.h>
+
+#if defined(__loongarch_asx)
+#  include <lasxintrin.h>
+#  define CV_LASX 1
+#endif
+
+#if defined CV_LASX
+int test()
+{
+    const float src[] = { 0.0f, 1.0f, 2.0f, 3.0f, 4.0f, 5.0f, 6.0f, 7.0f };
+    v8f32 val = (v8f32)__lasx_xvld((const float*)(src), 0);
+    return __lasx_xvpickve2gr_w(__lasx_xvftint_w_s (val), 7);
+}
+#else
+#error "LASX is not supported"
+#endif
+
+int main()
+{
+  printf("%d\n", test());
+  return 0;
+}