fix warnings and errors in Config.in

boot/Config.in

@@ -1,2 +1,2 @@
-source package/uboot/Config.in
+source "package/uboot/Config.in"
-source package/grub2/Config.in
+source "package/grub2/Config.in"

package/dropbear/Config.in

@@ -5,4 +5,4 @@ config SIMPLE_PACKAGE_DROPBEAR
     help
         Embedded ssh server
 
-source package/sftp-server-dropbear/Config.in
+source "package/sftp-server-dropbear/Config.in"

toolchain/Config.in

@@ -1,8 +1,8 @@
 choice SIMPLE_SELECT_STANDARD_LIBRARY
     prompt "Select default C library"
-    default SIMPLE_UCLIBC
+    default SIMPLE_PACKAGE_UCLIBC
-source package/glibc/Config.in
+source "package/glibc/Config.in"
-source package/uclibc/Config.in
+source "package/uclibc/Config.in"
 endchoice
 
 config SIMPLE_CROSS_COMPILE