Apply squashfs filesystem to the initrd(ramdisk) of IOT

Apply squashfs filesystem to the initrd(ramdisk) of IOT

squashfs supports compression.

=====================================
| ext4 (M byte) | squashfs (M byte) |
====================================|
|      6.5      |       3.7         |
|     10.0      |       5.5         |
-------------------------------------
|     13.0      |       7.0         |
|     13.4      |       7.3         |
-------------------------------------
|     13.8      |       7.7         |
|     14.3      |       7.9         |
-------------------------------------
|     15.0      |       8.2         |
|     16.3      |       9.1         |
=====================================

Change-Id: I07d2fed88494009cb7b19dc30ec4cdec1818a16f