ramdisk: Import ramdisk from Franco kernel
scripts: Add dtbTool and mkbootimg binaries

Taken from here: http://forum.xda-developers.com/showthread.php?t=2469510
build-sultan-kernel: Add additional steps to create boot.img with DTB support for MSM8974 devices

The commands here have information specific to the Nexus 5. Source for the commands themselves:

http://forum.xda-developers.com/showthread.php?t=2469510
http://forum.xda-developers.com/showthread.php?t=1413308

Signed-off-by: Sultanxda <sultanxda@gmail.com>
arch: arm: boot: Makefile: Add clean step for dt.img
Makefile: Add clean step for boot.img
.gitignore: Ignore *.img files
build-sultan-kernel: Rename boot.img to sultan.img