[Tosa] Fix legalization of BroadcastTo
Hi @jpienaar Can you please review this PR ? Thank you!
fix legalization of BroadcastTo by:
  - for floats: add with -0.0 (instead of 0.0)
  - for integer types other than I32, insert cast to I32, before adding zero, then cast back to output type 
    (because tosa add only supports I32 for integer types)
  - fixed lit tests for above changes as well


Change-Id: I93351250b18e4a318aa67c7029948bf3ab022533