Sync tf_config files with internal CI

Signed-off-by: Zelalem <zelalem.aweke@arm.com>
Change-Id: I064f4f252fe7d3770719dee040feb96ea180a9bb
diff --git a/tf_config/rk3399-coreboot b/tf_config/rk3399-coreboot
new file mode 100644
index 0000000..bc9294a
--- /dev/null
+++ b/tf_config/rk3399-coreboot
@@ -0,0 +1,3 @@
+COREBOOT=1
+CROSS_COMPILE=aarch64-none-elf-
+PLAT=rk3399