riscv: Add SMP Kconfig option dependency for U-Boot proper

U-Boot proper running in S-mode only need SMP support when using
SBI v0.1. With SBI v0.2 HSM extension, it does not need implement
multicore boot in U-Boot proper.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 5ef6849..a252cdb 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -193,6 +193,7 @@
 
 config SMP
 	bool "Symmetric Multi-Processing"
+	depends on SBI_V01 || !RISCV_SMODE
 	help
 	  This enables support for systems with more than one CPU. If
 	  you say N here, U-Boot will run on single and multiprocessor