common: add support to sign boot image

adding rules for generating signed boot image

Change-Id: I53710c2b4b8e8750c29d9c46c51a3e4ff0f270d2
Merge "common: add support to sign boot image"
Merge 214c259185d4c294e5b808ad1c6c44d307a8d786 on remote branch

Change-Id: I2dd17eb7e30e33063e9d4496e3d3d77a1bd8876d
Merge "Merge 214c259185d4c294e5b808ad1c6c44d307a8d786 on remote branch"