support/testing/tests/boot/test_atf: DTC needed for ATF Vexpress test

Since the bump of ATF to 2.2 for the ATF Vexpress test case in commit
fc3d6a3ed0f5f1ceda7ab64b8b2bee88abd29373
("support/testing/tests/boot/test_atf: update U-Boot/ATF use in
TestATFVexpress"), DTC is now needed otherwise the build fails with:

make[2]: dtc: Command not found
Makefile:873: recipe for target 'build/juno/release/fdts/juno_tb_fw_config.dtb' failed

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/674934470

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

support/testing/tests/boot/test_atf.py

@@ -14,6 +14,7 @@ class TestATFVexpress(infra.basetest.BRTest):
         BR2_TARGET_ARM_TRUSTED_FIRMWARE_PLATFORM="juno"
         BR2_TARGET_ARM_TRUSTED_FIRMWARE_FIP=y
         BR2_TARGET_ARM_TRUSTED_FIRMWARE_UBOOT_AS_BL33=y
+        BR2_TARGET_ARM_TRUSTED_FIRMWARE_NEEDS_DTC=y
         BR2_TARGET_UBOOT=y
         BR2_TARGET_UBOOT_BOARDNAME="vexpress_aemv8a_juno"
         BR2_TARGET_UBOOT_CUSTOM_VERSION=y