d/targets: Enable support for am625-sk

Enable building of U-Boot components for TI Sitara systems and the AM625 development board (known as the AM62-SK or am62x_evm in U-Boot). This platform boots initially via a 32-bit ARM core, a U-Boot SPL running there then initialises the 64-bit cores. Linux is not run on the aforementioned 32-bit core, so to avoid needing to enable the 32-bit ARM arch to gain access to the required U-Boot build, the 32-bit binaries are cross compiled.

Additionally, to build the final boot firmware, U-Boot is combined with various other components, such as ATF and some TI provided firmware. At the moment this firmware has not been submitted for inclusion in linux-firmware, so for now we are just building the U-boot components and patching out generation of the final boot firmware.

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