ewaol-bsp/n1sdp: Fix ewaol-virtualization-sdk-image build

We also need to append the ewaol-virtualization-sdk-image recipe to include
the extra dependency on xen and xen-devicetree deploy for generating the wic
image.

Issue-Id: SCM-3910
Signed-off-by: Diego Sueiro <diego.sueiro@arm.com>
Change-Id: I9608c1145ba963aaf580bc6faa4c0b0cfe2cb712