configs: phycore_am64x_a53_defconfig: Make BOOTCMD generic

The phyCORE-AM64x board code sets an environment variable 'boot'
with the device U-Boot booted from. Use this variable in
CONFIG_BOOTCOMMAND to boot Linux from the same boot device by
default.

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