plat(juno): use generic image fetching functions

Some generic functions have been provided for fetching prebuilt images -
use these for Juno runs.

Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
Change-Id: I77c1a0e3336ecdbbdba88078b8ee6e03dc760b0f
diff --git a/run_config/juno-linux.uboot b/run_config/juno-linux.uboot
index 38ddb69..a6ceba0 100644
--- a/run_config/juno-linux.uboot
+++ b/run_config/juno-linux.uboot
@@ -6,7 +6,7 @@
 #
 
 post_tf_build() {
-	get_scp_bl2_bin
+	url="${scp_bl2_url}" filename="scp_bl2.bin" fetch_and_archive
 	get_ml_uboot_bin
 	build_fip BL33="$archive/uboot.bin" SCP_BL2="$archive/scp_bl2.bin"
 }