plat(fvp): use generic image fetching functions

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

Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
Change-Id: I785890c9b0370279230dfd6f71a54bcdc0ebc9c3
diff --git a/run_config/fvp-optee b/run_config/fvp-optee
index 4419064..85e71c3 100644
--- a/run_config/fvp-optee
+++ b/run_config/fvp-optee
@@ -6,5 +6,5 @@
 #
 
 post_tf_build() {
-	get_optee_bin
+	url="$tfa_downloads/optee/tee.bin" filename="bl32.bin" fetch_and_archive
 }