riscv: Make SYS_SUPPORTS_HUGETLBFS depends on MMU

HUGETLBFS only used when MMU enabled, add the dependency.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -136,6 +136,7 @@ config ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	def_bool y
 
 config SYS_SUPPORTS_HUGETLBFS
+	depends on MMU
 	def_bool y
 
 config STACKTRACE_SUPPORT