kernel: skip installing fitImage when using Initramfs bundles

kernel: skip installing fitImage when using Initramfs bundles

When including an initramfs bundle inside a FIT image, the fitImage is created
after the install task by do_assemble_fitimage_initramfs.

This happens after the generation of the initramfs bundle
(done by do_bundle_initramfs).

So, at the level of the install task we should not try to install the fitImage.
The fitImage is still not generated yet.

After the generation of the fitImage, the deploy task copies the fitImage from
the build directory to the deploy folder.

Change-Id: I3eaa6bba1412f388f710fa0f389f66631c1c4826
Signed-off-by: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>