chromebook: Add rev5 to fit image creation

Add the rev5 snow board to the fit image, and remove spring, since it needs it's own nv-uboot and kernel.
hp-chromebook: Add initial script for building "spring" images.

Spring is the codename for the HP Chromebook.  The only differences between it and the Samsung ARM Chromebook are a different dtb file for the fit image, and a different nv_uboot image.
all: sha1sum fixes

Previously, the sha1sum command was including the path to the files.  This isn't necessary, so remove it, and gives us the advantage of sha1sum checking working when the file isn't in the exact path that it was built.
efikamx: Fix typo in boot.script

There was a typo in the boot.script.  Even though we don't use a uInitrd, it's there for people who might want to
Merge pull request #1 from steev/master

Updates for Chromebook script and add the HP Chromebook script