common: add support to sign boot image

adding rules for generating signed boot image

Change-Id: I53710c2b4b8e8750c29d9c46c51a3e4ff0f270d2
Sign recovery image

LK now requires recovery image to be signed. This
is a new change to ensure that only signed images
are used.

Change-Id: I25fef9c311370e3f26d2d09b577575cd2a16f880
Merge "Sign recovery image"
Merge "common: add support to sign boot image"
Merge f1def605815549d151fe887d97766e5fd8cc8ff7 on remote branch

Change-Id: I1a0178b08c28794024552f0c5a6e1db5ad597a8f
Merge "Merge f1def605815549d151fe887d97766e5fd8cc8ff7 on remote branch"
Merge commit 'AU_LINUX_ANDROID_LNX.LA.3.7.2_RB1.04.04.04.156.020' on remote branch

Change-Id: I9b91f29241a1f846419e87224e498ba2e9176e7c
Merge "Merge commit 'AU_LINUX_ANDROID_LNX.LA.3.7.2_RB1.04.04.04.156.020' on remote branch"