test: Set the DTC environment variable

Set this to our own device-tree compiler since we know it is new enough to
run the tests.

Signed-off-by: Simon Glass <sjg@chromium.org>

test/run

@@ -17,17 +17,19 @@ run_test ./test/py/test.py --bd sandbox_spl --build -k \
 # Run tests for the flat DT version of sandbox
 ./test/py/test.py --bd sandbox_flattree --build
 
-PYTHONPATH=build-sandbox_spl/scripts/dtc/pylibfdt run_test \
+DTC_DIR=build-sandbox_spl/scripts/dtc
+
+PYTHONPATH=${DTC_DIR}/pylibfdt DTC=${DTC_DIR}/dtc run_test \
 	./tools/binman/binman -t
 run_test ./tools/patman/patman --test
 run_test ./tools/buildman/buildman -t
-PYTHONPATH=build-sandbox_spl/scripts/dtc/pylibfdt run_test ./tools/dtoc/dtoc -t
+PYTHONPATH=${DTC_DIR}/pylibfdt DTC=${DTC_DIR}/dtc run_test ./tools/dtoc/dtoc -t
 
 # This needs you to set up Python test coverage tools.
 # To enable Python test coverage on Debian-type distributions (e.g. Ubuntu):
 #   $ sudo apt-get install python-pip python-pytest
 #   $ sudo pip install coverage
-PYTHONPATH=build-sandbox_spl/scripts/dtc/pylibfdt run_test \
+PYTHONPATH=${DTC_DIR}/pylibfdt DTC=${DTC_DIR}/dtc run_test \
 	./tools/binman/binman -T
 
 if [ $result == 0 ]; then