Improve CTS coverage of bf16 elementwise binary ops

Included ops: ADD, SUB, MUL, POW, MINIMUM, MAXIMUM

- Full rank coverage
- Also add rank 6 for tosa-pro-fp in some ops

Signed-off-by: Ian Tayler Lessa <ian.taylerlessa@arm.com>
Change-Id: I22c4ca9e96b440e3d5b89a4c76a5f110aca99e47