[idea] deviceside detectfield

[iceman1001]

I know, this is a detectfield already. It is not what I am thinking of.
If you examine the device source code you find some bits and pieces in the sim HF code that it tries to detect a drop in the voltage and that it taken as a indication that the reader is in proximity and we can start simulate.

What I'm thinking of is to make that detection more generic, and extracted to a function as it can be easily to add to other parts. Not just those places which implements it.

ref:
https://github.com/iceman1001/proxmark3/blob/master/armsrc/iso14443a.c#L3047