core-image-tiny-initramfs: Add and image creating image artifacts only

core-image-tiny-initramfs: Add and image creating image artifacts only

Add an image that simply creates image artifacts using
image-live-artifacts support instead of creating an actual image.

The image artifacts can then be subsequently assembled by an external
tool such as wic to create an actual image.

This eliminates redundant image creation when using such tools.

Signed-off-by: Alejandro Hernandez <alejandro.hernandez@linux.intel.com>
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>