Fix IHEX firmware generation/loading

Fix both the IHEX firmware generation (len field always null, and EOF
marker a byte too short) and loading (struct ihex_binrec needs to be
packed to reflect the on-disk structure).

Signed-off-by: Marc Zyngier <maz@misterjones.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>