boot: bootutil: Fix serial recovery issues

Fixes serial recovery issues in various MCUboot operating modes by
moving functions that are needed out from loader to a common file
and adapting them to work in these different modes

Note: This PR has been modified from the upstream commit due to
a merge failure from other changes that are not being brought into
Zephyr 3.7

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
(cherry picked from commit e2c97da3)