cca_defconfig: Enable reproducible builds

Try to generate the same initrd every time, so we only need to provision
the verifier once.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>

configs/cca_defconfig

@@ -26,3 +26,7 @@ BR2_PACKAGE_REALM_TOKEN=y
 BR2_PACKAGE_CCA_WORKLOAD_ATTESTATION=y
 
 BR2_ROOTFS_POST_BUILD_SCRIPT="$(BR2_EXTERNAL_LINARO_CCA_PATH)/scripts/post-build.sh"
+
+# Try to generate the same image every time, so we only need to provision
+# the verifier with an initrd hash once.
+BR2_REPRODUCIBLE=y