cmd: CMD_ACPI depends on ACPIGEN

Trying to compile qemu-x86_64_defconfig with CONFIG_CMD_ACPI=y and
CONFIG_ACPIGEN=n fails with

ld.bfd: cmd/built-in.o: in function `do_acpi_items':
cmd/acpi.c:162: undefined reference to `acpi_dump_items'

Add the missing configuration dependency.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

cmd/Kconfig

@@ -84,7 +84,8 @@ menu "Info commands"
 
 config CMD_ACPI
 	bool "acpi"
-	default y if ACPIGEN
+	depends on ACPIGEN
+	default y
 	help
 	  List and dump ACPI tables. ACPI (Advanced Configuration and Power
 	  Interface) is used mostly on x86 for providing information to the