Makefile: unexport 'DEVICE_TREE' environment variable
U-Boot looks for the environment variable DEVICE_TREE and uses its value if
set instead of the CONFIG_DEFAULT_DEVICE_TREE configuration option since
v2021.01, more specifically commit c0f1ebe9c1b9745e (binman: Allow selecting
default FIT configuration) - So unexport it like we do for other
"troublesome" environment variables to ensure consistent behaviour.
Reported-by: Neal Frager <nealf@xilinx.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Peter Korsgaard