kernel-fitImage: Take possible multiconfig into account.

kernel-fitImage: Take possible multiconfig into account.

When specifying the dependencies of do_assemble_fitimage_initramfs the
initramfs image might be built with another multiconfig. This needs to be
taken into account.

The path of the initramfs image also needs to be adapted to handle the
case when it's built with another multiconfig.

Signed-off-by: Weisser, Pascal <pascal.weisser.ext@karlstorz.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>