MLBEDSW-10310: MLCE: Wrong ofm shape for Prelu ops implemented by AvgPool

 - An Avgpool with the wrong ofm shape caused an output difference
 - The wrong shape is caused by the removal of a Reshape op causing
 the Prelu actual op ofm shape and tensor shape to differ
 - Prelu was then later converted the an AvgPool with an faulty value on
the op ofm shape (using the Reshape output shape)
 - The fix is to make sure the original Prelu output shape is used for
 the AvgPool

Change-Id: I878695cbac2e9c0a5323eb7f620047588454b138
Signed-off-by: Johan Alfvén <johan.alfven@arm.com>