lib: fs_mgr: fix parsing twrp's unhandled flags

I forgot to add spacec between all the flags.
parse mmc partitions in /sys/class/block

this allows us to check which partition GRUB is installed to.
This way we can convert the mount of this partition to a bind mount inside fstabs
improve debugging

- correctly use log levels instead of random ones
- allow to change debug level via "multiboot.debug" in cmdline