kbuild: create symbolic link only for ARM, AVR32, SPARC, PowerPC, x86

The symbolic link to SoC/CPU specific header directory is created
during the build, while it is only necessary for ARM, AVR32, SPARC,
x86, and some CPUs of PowerPC.  For the other architectures, it just
results in a broken symbolic link.

Introduce CONFIG_CREATE_ARCH_SYMLINK to not create unneeded symbolic
links.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 3b3f446..18451d3 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -22,9 +22,11 @@
 
 config MPC83xx
 	bool "MPC83xx"
+	select CREATE_ARCH_SYMLINK
 
 config MPC85xx
 	bool "MPC85xx"
+	select CREATE_ARCH_SYMLINK
 
 config MPC86xx
 	bool "MPC86xx"
@@ -34,6 +36,7 @@
 
 config 4xx
 	bool "PPC4xx"
+	select CREATE_ARCH_SYMLINK
 
 endchoice