Add matrix multiplication test
- Add reference implementation for packing LHS, RHS, and the main matmul routine.
- Add test for matrix multiplication:
- Generic test is implemented for all matmul methods.
- The test checks the arbitrary portion of the output matrix.
- The test checks the LHS packing, RHS packing and the main matmul kernels.
Signed-off-by: Viet-Hoa Do viet-hoa.do@arm.com