Split MicroSMP diode footprint into _AK and _KA variants

EDIT: As eventually clarified, some MicroSMP diodes have a large-pad-anode and some a large-pad-cathode orientation. This PR now splits the footprint into the two variants occurring in the wild.

Original title: Fix MicroSMP diode footprint (the larger pad is the anode)

This is a fix for !2921 (merged); I apparently mixed up the anode (actually the large one) and cathode (actually the small one) pad. Apologies!