core(intrin): avoid symbols duplication from SIMD128/256 cases

All vx_call() must be wrapped into own simd128/simd256/simd512 namespace

```
namespace CV__SIMD_NAMESPACE {
... vx_call declaration is here ...
}
```

modules/core/include/opencv2/core/hal/intrin.hpp

@@ -296,11 +296,17 @@ template<typename _Tp> struct V_RegTraits
 #endif
 
 #if CV_SIMD512 && (!defined(CV__SIMD_FORCE_WIDTH) || CV__SIMD_FORCE_WIDTH == 512)
+#define CV__SIMD_NAMESPACE simd512
+namespace CV__SIMD_NAMESPACE {
     #define CV_SIMD 1
     #define CV_SIMD_64F CV_SIMD512_64F
     #define CV_SIMD_WIDTH 64
     // TODO typedef v_uint8 / v_int32 / etc types here
+} // namespace
+using namespace CV__SIMD_NAMESPACE;
 #elif CV_SIMD256 && (!defined(CV__SIMD_FORCE_WIDTH) || CV__SIMD_FORCE_WIDTH == 256)
+#define CV__SIMD_NAMESPACE simd256
+namespace CV__SIMD_NAMESPACE {
     #define CV_SIMD 1
     #define CV_SIMD_64F CV_SIMD256_64F
     #define CV_SIMD_WIDTH 32
@@ -323,7 +329,11 @@ template<typename _Tp> struct V_RegTraits
     CV_INTRIN_DEFINE_WIDE_INTRIN_ALL_TYPES(v256)
     CV_INTRIN_DEFINE_WIDE_INTRIN(double, v_float64, f64, v256, load)
     inline void vx_cleanup() { v256_cleanup(); }
+} // namespace
+using namespace CV__SIMD_NAMESPACE;
 #elif (CV_SIMD128 || CV_SIMD128_CPP) && (!defined(CV__SIMD_FORCE_WIDTH) || CV__SIMD_FORCE_WIDTH == 128)
+#define CV__SIMD_NAMESPACE simd128
+namespace CV__SIMD_NAMESPACE {
     #define CV_SIMD CV_SIMD128
     #define CV_SIMD_64F CV_SIMD128_64F
     #define CV_SIMD_WIDTH 16
@@ -348,6 +358,8 @@ template<typename _Tp> struct V_RegTraits
     CV_INTRIN_DEFINE_WIDE_INTRIN(double, v_float64, f64, v, load)
     #endif
     inline void vx_cleanup() { v_cleanup(); }
+} // namespace
+using namespace CV__SIMD_NAMESPACE;
 #endif
 
 inline unsigned int trailingZeros32(unsigned int value) {