Add AArch32 to the boot-wrapper

This patch allows to build a 32-bit boot-wrapper, and create a complete
linux-system.axf for models that start in AArch32. Most of the code is a
simple translation of the AArch64 side.

We add an --aarch32-bw argument to ./configure, and bump the version to
0.2, to welcome this new architecture.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>