IVGCVSW-7937 Review and update documentation related with new operators for 23.11

* GELU added to activation operators, despite not being part of Android NDK
* BROADCAST_TO added to layers, despite not being implemented in any backend
* CAST SIGNED64 added

Change-Id: I32edb9939d28cb997432762e8ea5904f92c12687

Signed-off-by: Teresa Charlin <teresa.charlinreyes@arm.com>
Change-Id: I6a27ebc1233d77522c1bed1c7e89df95e4d55177