device/msm8916*: Generate extlinux.conf for armv7 devices as well

!4826 (merged) was meant to update all users of msm8916 kernel but I've missed the fact that apk list -d only showed me the users for the current arch (which was aarch64) but we also have some armv7 users too... Oops...

This MR repeats the same steps for armv7 users of the msm8916 kernel.

Notably this includes few msm8909 devices for which using "future" lk2nd is actually required.