riscv: Fix print_vm_layout build error if NOMMU

arch/riscv/mm/init.c: In function ‘print_vm_layout’:
arch/riscv/mm/init.c:68:37: error: ‘FIXADDR_START’ undeclared (first use in this function);
arch/riscv/mm/init.c:69:20: error: ‘FIXADDR_TOP’ undeclared
arch/riscv/mm/init.c:70:37: error: ‘PCI_IO_START’ undeclared
arch/riscv/mm/init.c:71:20: error: ‘PCI_IO_END’ undeclared
arch/riscv/mm/init.c:72:38: error: ‘VMEMMAP_START’ undeclared
arch/riscv/mm/init.c:73:20: error: ‘VMEMMAP_END’ undeclared (first use in this function);

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/mm/init.c

@@ -47,7 +47,7 @@ static void setup_zero_page(void)
 	memset((void *)empty_zero_page, 0, PAGE_SIZE);
 }
 
-#ifdef CONFIG_DEBUG_VM
+#if defined(CONFIG_MMU) && defined(CONFIG_DEBUG_VM)
 static inline void print_mlk(char *name, unsigned long b, unsigned long t)
 {
 	pr_notice("%12s : 0x%08lx - 0x%08lx   (%4ld kB)\n", name, b, t,