intel/mi: Optimize away LOAD_REGISTER_REG from a register to itself

intel/mi: Optimize away LOAD_REGISTER_REG from a register to itself

We might want to resolve something to be in a particular register,
so we can access it outside of the gen_mi framework...but it may already
be in that register, at which point there's no work to do.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>