kernelscripts: Create separate directories for secondary images

Create separate directories for primary and secondary images,
so that the binaries are placed into the correct locations
when they are generated, and so the correct binaries are
used when they are needed.

Change-Id: Ibf636e035da04dd720146140e0ec7f9cc0504c8c
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>