riscv: cpu: fu540: Add support for cpu fu540

Add SiFive fu540 cpu to support RISC-V arch

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index fb5fe5a..d9854f5 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -56,6 +56,7 @@
 
 # platform-specific options below
 source "arch/riscv/cpu/ax25/Kconfig"
+source "arch/riscv/cpu/fu540/Kconfig"
 source "arch/riscv/cpu/generic/Kconfig"
 
 # architecture-specific options below