normal zip limit is 4GB, but due to signed variables it will only
access 2GB (32bit signed integer is from -2GB to +2GB).

these changes allow for a theoretical limit of 4GB zips to be flashed.
RAM restrictions still apply, and on a 32bit system it's likely to max
out at approx 2.8GB flashable zip, above that mmap will probably fail.

Note: the flashable zip also needs a compatible update-binary which
include these changes.
(this also applies to both aroma installer if it's being used).

Change-Id: Ib3af2945c9bd4890a2e6dc45acfc2b80ec55473b