Add user example for FP16 MatMul using Arm® Neon™

This example demonstrates the usage of the FP16 packing and matmul routines which:

1. Packs the bias and the weights together into a single tensor.

2. Performs a matrix multiplication of the activations and the packed tensor.

All tensors are in half precision floating-point (FP16) data type.

Signed-off-by: Jakub Sujak <jakub.sujak@arm.com>

Reviewed-by: Jakub Sujak <jakub.sujak@arm.com>
Approved-by: Felix Johnny Thomasmathibalan <felixjohnny.thomasmathibalan@arm.com>