pan/bi: Lower transcendentals on G71

So people stop asking... I didn't actually setup a G71 board so this is tested on G52 but hey, it 'should' work, right?

Huge kudos to @cwabbott0 for figuring this out. frcp/frsq/fexp2 algorithms match the blob, per cwabbott's descriptions. flog2 doesn't quite match (this code uses a lower-degree polynomial ==> probably not precise enough) but I don't care enough about G71 to fix it, and I was having troubles implementing the algorithm as stated. So.. good enough for now. It passes the tests.