main/postmarketos-initramfs: add support for multi-device btrfs
This change fixes booting with a multi-device btrfs volume as root filesystem. A multi-device btrfs volume will find all partitions or devices automatically when mounted, but this only works if btrfs device scan
was run beforehand.
This adds a call to btrfs device scan
before mounting if the root filesystem is btrfs
.
The command will only run for btrfs root filesystems, so I consider this change fairly safe.