am62x: Add U-Boot installation image and delete image-am62x.yaml

In order to simplify the process of installing U-Boot on the AM62-SK eMMC hardware boot partition, create an image that can be run from the SDCard to automate the process.

This enables the am62x, specifically the SK-AM62 development board used during development, to boot the standard U-Boot image. With this in place, this mechanism is the preferred way of booting Apertis on the SK-AM62 and the image-am62x.yaml recipe is redundant.

Signed-off-by: Martyn Welch martyn.welch@collabora.com