Do you have a 4.12 DT with the SD card working and, if so, can you post it somewhere? Also, can you post the precise firmware blobs you’re using?
Also, were you able to get mwifiex working with multiple phys for 5GHz and 2.4? I briefly managed to get mwifiex working at one point, but as far as I can tell, the number of phys in mwifiex is fixed at 1 and you have to pick between 5 and 2.4 (whereas the marvell driver lets you do both). I suppose if you have 4.12 working I can try mwlwifi, though.