COMPMID-3464: Address NESoftmaxLayer failures for QASYMM8_SIGNED

COMPMID-3464: Address NESoftmaxLayer failures for QASYMM8_SIGNED

Normalization with the maximum value was causing results to wrap-around
As a work-around we use saturating intrinsics to perform the operation

Signed-off-by: Georgios Pinitas <georgios.pinitas@arm.com>
Change-Id: I719b7ac7ad274dc2ae339bc4a055f9200134ed97
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/3184
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Sang-Hoon Park <sang-hoon.park@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>