[mlir][tosa] Improve lowering support for tosa.concat

The existing lowering for tosa.concat fails in some instances when the
output shape contains more information the input shapes. The result is
an illegal tensor.empty operation.

This change bases the output shape on the original tosa.concat
operation, while querying the input tensor shapes to build the slicing
operations.

Reviewed By: rsuderman

Differential Revision: https://reviews.llvm.org/D151707