cli: Allow installing modules for RAW kernel package type

Add a "modules" attribute within the plan's "config" object (and add
--modules option to "fastpath sut install"). This is allowed only when
pkgtype is "RAW" (either implicitly or explicitly).

When present, fastpath will explicitly install the modules along with
the kernel image. It's been tested with kernel image and modules
produced by Kernel CI, tuxmake and shrinkwrap.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>