AMDGPU: Refactor mfma hazard handling [NFC]

Try to make this editable by using functions for the number
of wait states as a function of the number of passes. I'm assuming
the current hazard test coverage is comprehensive.

This could probably use another round to further simplify it.
Alternatively, I believe this could all be expressed in a constant
table indexed by an instruction classify function and number of passes.

Author: arsenm