support/testing: TestATFMarvell needs BR2_TARGET_UBOOT_NEEDS_DTC=y

The Marvell U-Boot needs DTC to build, so the test case fails to build
on systems where dtc isn't available. We add
BR2_TARGET_UBOOT_NEEDS_DTC=y to make sure that we build our own DTC.

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/44126707

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

support/testing/tests/boot/test_atf.py

@@ -73,6 +73,7 @@ class TestATFMarvell(infra.basetest.BRTest):
     BR2_TARGET_UBOOT_BOARDNAME="mvebu_mcbin-88f8040"
     BR2_TARGET_UBOOT_CUSTOM_VERSION=y
     BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2017.09"
+    BR2_TARGET_UBOOT_NEEDS_DTC=y
     """
 
     def test_run(self):