toolchain: rename external toolchain dir

Rename the external toolchain directory.
When new backends are here, it will be easier to sort them out
if they are all prefixed the same way.

Signed-off-by: Yann E. MORIN <yann.morin.1998@anciens.enib.fr>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/Config.in

@@ -17,7 +17,7 @@ config BR2_TOOLCHAIN_EXTERNAL
 endchoice
 
 source "toolchain/Config.in.1"
-source "toolchain/external-toolchain/Config.in"
+source "toolchain/toolchain-external/Config.in"
 
 # we want gdb config in the middle of both source and external
 # toolchains, but mconf won't let us source the same file twice,
@@ -26,6 +26,6 @@ source "toolchain/gdb/Config.in"
 comment "Common Toolchain Options"
 
 source "toolchain/Config.in.2"
-source "toolchain/external-toolchain/Config.in.2"
+source "toolchain/toolchain-external/Config.in.2"
 
 endmenu