btrfs-progs: export is_ssd()

  Move is_ssd() to utils.c and export it in order
that the functions in other files can also take use
of it.

Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>
btrfs-progs: add hot relocation support in mkfs

  Introduce one new mkfs.btrfs option (-h) for hot
relocation which preallocate two new block group type
BTRFS_BLOCK_GROUP_DATA_SSD.

Signed-off-by: Ben Chociej <bchociej@gmail.com>
Signed-off-by: Matt Lupfer <mlupfer@gmail.com>
Signed-off-by: Zhi Yong Wu <wuzhy@linux.vnet.ibm.com>