[archiso] Add btrfs support as filesystem for *.fs.sfs

Implements FS#30378

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

README

@@ -396,6 +396,7 @@ EOF
  + squashfs-tools          for mksquashfs
  + libisoburn              for xorriso
  + rsync                   for rsync
+ + btrfs-progs             for mkfs.btrfs (optional)
 
 ** For configs/releng build.sh needs theses packages (build host):
  + dosfstools              for mkfs.vfat

archiso/mkarchiso

@@ -298,7 +298,7 @@ _mksfs () {
 
 # Makes a filesystem from a source directory.
 # $1: Source directory
-# $2: Target filesystem type (ext4 | ext3 | ext2 | xfs)
+# $2: Target filesystem type (ext4 | ext3 | ext2 | xfs | btrfs)
 # $3: Size of target filesystem. Can be an absolute value in MiB, or relative value of desired free space (1% - 99%)
 _mkfs () {
     local _src="${1}"
@@ -351,6 +351,9 @@ _mkfs () {
         xfs)
             mkfs.xfs ${_qflag} "${_fs_img}"
             ;;
+        btrfs)
+            mkfs.btrfs -M "${_fs_img}"
+            ;;
         *)
             _msg_error "Invalid filesystem: ${_fs_type}" 1
             ;;