apps/nshlib: Tighten up some of the conditional logic for mkrd.

nshlib/Kconfig

@@ -12,7 +12,7 @@ config NSH_LIBRARY
 	select NETUTILS_NETLIB if NET
 	select LIBC_NETDB if NET
 	select READLINE_HAVE_EXTMATCH
-	select DRVR_MKRD if !NSH_DISABLE_MKRD
+	select DRVR_MKRD if !NSH_DISABLE_MKRD && !DISABLE_MOUNTPOINT
 	---help---
 		Build the NSH support library.  This is used, for example, by
 		system/nsh in order to implement the full NuttShell (NSH).

nshlib/nsh.h

@@ -861,13 +861,24 @@ int nsh_loginscript(FAR struct nsh_vtbl_s *vtbl);
 #endif
 #endif
 
-/* Architecture-specific initialization */
+/* Certain commands are only available if the boardctl() interface is
+ * available:
+ */
+
+/* Architecture-specific initialization depends on boardctl(BOARDIOC_INIT) */
 
 #if defined(CONFIG_NSH_ARCHINIT) && !defined(CONFIG_LIB_BOARDCTL)
 #  warning CONFIG_NSH_ARCHINIT is set, but CONFIG_LIB_BOARDCTL is not
 #  undef CONFIG_NSH_ARCHINIT
 #endif
 
+/* The mkrd command depends on boardctl(BOARDIOC_MKRD) */
+
+#if !defined(CONFIG_LIB_BOARDCTL) || !defined(CONFIG_DRVR_MKRD)
+#  undef CONFIG_NSH_DISABLE_MKRD
+#  define CONFIG_NSH_DISABLE_MKRD 1
+#endif
+
 /* Basic session and message handling */
 
 struct console_stdio_s;