gpttool: useful for partitioning sdcards

Where @partitions.txt contains:

:128k

xloader:128k
bootloader:256k
environment:128k
:384k
boot:8m
recovery:8m
system:256m
cache:256m
userdata:1g

Change-Id: I1221677e5b3dc4d5b19420c4a64d21b587fb7d47
media: