sbtools: add brute force option for sb1 in sbtoelf

After some reverse engineering, it appears that the keys of the
sb1 format are very weak: the 128 bytes are generated from the
laserfuse words 4,5 and 6 but in a weird manner: 4 and 5 are
simply ORed and 6 is only half used (somehow), making it "only" a
48 bit word to find.

Change-Id: I40702e19d0924ef51c01894efce3cb65bd664456
6 files changed