zynq: convert to new image build code

zynq: convert to new image build code

Convert the Zynq target to use the new image build code in order to fix
broken image generation after 9945a1dca5bb6bc522393f7583baf3a64df6ce11
changed the handling of CPIO images.

Also remove the misapplied ubifs feature flag since the image generation is
not using UBIFS for building FIT images.

As part of the conversion, move the DTB building and the uImage ramdisk
generation into separate build steps which can be generalized and shared
with other targets, like APM821xx, in the long run.

Also remove the legacy profile declarations and use new-style per-device
profiles which will allow different package sets per image in the future.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>