board: phytec: phycore_am64x: Add Network/SPI Boot

Include the boot logic to boot via Network or from a OSPI/QSPI
NOR flash. Moreover, set all required variables to both boot
methods to the environment.

Note: The phyBOARD-Electra AM64x is not able to load the U-Boot
via Network. However, it's still possible to load the kernel.

Signed-off-by: Daniel Schultz <d.schultz@phytec.de>
1 file changed