util/xcompile: prefer riscv64 over riscv

gcc 8.1 insists.

Change-Id: I8cb00fafdfff7679e38f357c6e8968da656c351d
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Reviewed-on: https://review.coreboot.org/25995
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/xcompile/xcompile

@@ -334,7 +334,7 @@ arch_config_arm64() {
 arch_config_riscv() {
 	TARCH="riscv"
 	TBFDARCHS="littleriscv"
-	TCLIST="riscv riscv64"
+	TCLIST="riscv64 riscv"
 	TWIDTH="64"
 	TABI="elf"
 }