main/postmarketos-initramfs: start mdev/udev before setting up USB

There might be additional kernel modules needed for the USB UDC to show up. This used to work fine, but broke when the initramfs was unified with the minimal one. We need to load modules/start udev before setting up USB.

Fix this by duplicating the setup calls in both init.sh and init_2nd.sh. Both calls already have checks to allow calling them multiple times, so we don't need to handle the initramfs-extra case in a special way.

Cc: @caleb @craftyguy @TravMurav