kernel.bbclass: remove dependency on initramfs when not bundled

kernel.bbclass: remove dependency on initramfs when not bundled

Previously, the kernel recipe depended on the initramfs image even when
INITRAMFS_IMAGE_BUNDLE was not enabled. This caused the kernel to be
rebuilt whenever the initramfs image changed, regardless of whether the
kernel actually included the initramfs.

The problematic chain was:
  linux:do_deploy ->
  linux:do_bundle_initramfs ->
  image-initramfs:do_image_complete

The original intent (acc. to the comment) was to ensure the initramfs
image was available for tools like wic. However, apart from bundling the
initramfs in the kernel, there is probably no reason why the kernel
should depend on the initramfs. And it is therefore simply wrong if it
does so anyway. Thus, use cases that may be broken by these change are
based on a bug, not a feature. This needs to be fixed by adding a
dependency on the initramfs in the right place, not in the kernel where
this destroys the kernel's sstate-caching.

Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>