RISC-V: Make NUMA depend on SMP

In theory these are orthogonal, but in practice all NUMA systems are
SMP.  NUMA && !SMP doesn't build, everyone else is coupling them, and I
don't really see any value in supporting that configuration.

Fixes: 4f0e8eef ("riscv: Add numa support for riscv64 platform")
Suggested-by: NAndrew Morton <akpm@linux-foundation.org>
Suggested-by: NAtish Patra <atishp@atishpatra.org>
Reported-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Tested-by: N Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NPalmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -314,6 +314,7 @@ endchoice
 # Common NUMA Features
 config NUMA
 	bool "NUMA Memory Allocation and Scheduler Support"
+	depends on SMP
 	select GENERIC_ARCH_NUMA
 	select OF_NUMA
 	select ARCH_SUPPORTS_NUMA_BALANCING