Add erofs bootfs support

[Eric Curtin]

In Fedora/CentOS Stream 9, /boot will be vfat or ext4 (there is talk of unifying /boot/efi and /boot into one partition in Fedora, a vfat one, vfat is mandatory for firmware as all UEFI firmwares implement this fs). But in an Android Boot environment at least, among others, erofs is also an option for the boot partition (which will probably be implemented in system_b label, with system_a label being rootfs).

Performing some simple benchmarks;

Mount speed:

1. vfat/erofs (very close, pretty much equal)
2. ext4

Read speed:

1. ext4
2. erofs
3. vfat

Mount speed is of utmost important for a quick boot. So read speed is the next decisive factor. Given that erofs has more potential to improve than vfat, in performance driven environments like an Android Bootloader based automotive environment, erofs makes sense for a boot partition. vfat also has a 4GB file limit, which can be limiting if you want to use that partition to store large files of some sort.