MLBEDSW-7654: Extend support for Mean where HxW > 4096

* Convert Means with large IFMs to several DeptwiseConv2DBias and Add
  operations.
* Update tflite supported operator check with new height and width
  constraints.
* Update unit-tests to verify supported operator changes.
* Fix output-diff for 2D IFMs (MLBEDSW-7772)

Signed-off-by: Alexander Hansson <Alexander.Hansson@arm.com>
Change-Id: Ifae6fb1cdac475ae7dac5116c5f13631ff82108a