Retire the ggml_mul_mat() branch for transposed src0 (#500)
* Retire the ggml_mul_mat() for transposed src0
- It can always be made contiguous with ggml_cpy()
- The code is now simplified
- The results are deterministic in respect to num threads
* SIMD-ify dequantize_row_q4_0() for ARM_NEON (#502)
* Attempt to SIMD-ify dequantize_row_q4_0() for ARM_NEON
* Fix dequantization - forgot to interleave the quants
