Re-purpose AV3 analog inputs for 2nd channel hall input (same as existing CAM)

[rusefi]

at the moment we have one Hall channel and one channel which could be either VR or hall depending on what resistors are mounter.

This hardware flexibility is quite labor intense, a nicer experience could be having one more hall-only channel and leave VR channel as VR only.

This would require selecting one more ICU input pin. We totally have ICU pin options (do we?)

microRusEfi AV3 channel (the one routed into stm32 PA7) should become the CAM2 hard-wired Hall channel

And technically we can confirm PAL input mode.