[FR] Lerdge K add support to second Z driver as EX-AXIS

Is your feature request related to a problem? Please describe.

Actually I have dual Z drivers and invidual Max Z homing sensors. On Lerdge original firmware it's possible using the Ex-Axis function as described in here: https://www.lerdge.com/document/detail/ExtensionOf-ExAxis

Are you looking for hardware support?

No response

Describe the feature you want

Would be nice if on Lerdge K Marlin firmware port one could choose to use Ex-Axis as: a) second individual step generator for Z axis (my setup) b) second step generator synchronized with steps on Z1 (some people use Ex-Axis like this)

This is a picture of my actual Ex-Axis configuration on Lerdge original firmware. Please, take this is consideration as it is the only thing attaching me to the Lerdge original firmware, which is awful.