modules: hal_ethos_u: Update for MPS4

What is changed?
  Added config for Ethos-U65 for Corstone315 which has default 256 MACs
  as per FVP.

Why do we need this change?
  This will help in validating the NPU when we add support for FVP
  testing for Ethos-U65.

Signed-off-by: Shaunak saha <ssaha@tsavoritesi.com>