riscv: Make NUMA depend on MMU

NUMA is useless when NOMMU, and it leads some build error,
make it depend on MMU.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -314,7 +314,7 @@ endchoice
 # Common NUMA Features
 config NUMA
 	bool "NUMA Memory Allocation and Scheduler Support"
-	depends on SMP
+	depends on SMP && MMU
 	select GENERIC_ARCH_NUMA
 	select OF_NUMA
 	select ARCH_SUPPORTS_NUMA_BALANCING