enabling support for simd256 and simd512 operations in prelu
This merge request has the following changes:
- enabling support for simd256 and simd512 operations in sadl/layer_prelu.h.
- Test models have been added to utests/models directory. They are present at utests/models/prelu_single_alpha_c32.onnx and utests/models/prelu_multiple_alpha_c32.onnx.
- utests/check.sh has been modified for the new prelu_single_alpha_c32.onnx and prelu_multiple_alpha_c32.onnx models.