riscv: fu540: enable SMP

Signed-off-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/board/sifive/fu540/Kconfig b/board/sifive/fu540/Kconfig
index 6be3d88..f464379 100644
--- a/board/sifive/fu540/Kconfig
+++ b/board/sifive/fu540/Kconfig
@@ -38,5 +38,6 @@
 	imply PHY_LIB
 	imply PHY_MSCC
 	imply SIFIVE_SERIAL
+	imply SMP
 
 endif