Config for building smaller hftest images

The size of hftest RAM disks may be too large for boards where we can
only use a small flash partition. Add a build arg for such boards and
try to build smaller binaries. This is best effort only.

Initially the config will strip out printing of details of failed
assertions, which requires keeping around many strings that cannot be
deduplicated. This saves about 25% on primary_with_secondaries tests.

Change-Id: I7af84e4298ffeddc7fd5c9bd4976d0234adc83bf
3 files changed