Split quantization reference implementation

* Split the dynamic quantization into two steps:
  - Computing the quantization information.
  - Quantizing the input data using the quantization information.
* The two functions will be used by tests for static quantization
  in the future.

Signed-off-by: Viet-Hoa Do <viet-hoa.do@arm.com>

Reviewed-by: Viet-Hoa Do <viet-hoa.do@arm.com>
Reviewed-by: Anton Bondarenko <anton.bondarenko@arm.com>
Approved-by: Anton Bondarenko <anton.bondarenko@arm.com>