Support incremental dev option OTA during signing

This allows incremental dev option to be used on release-key devices.
Boot images are signed during the signing process, and hence the dev
option OTAs(which are derivative of boot image) need to be re-generated.
Previously we only re-generate full OTAs, now we support incrementals
too.

Test: th
Bug: 339658378
Change-Id: I4755379b49ff8adf351ccaf76fe38f19c1685e9e