toolchain: make external toolchain the default for AArch64

Our internal toolchain backend does not yet have support for AArch64,
and Crosstool-NG also does not have support for AArch64 at the moment
(though it should be coming quickly since the Linaro AArch64 toolchain
is generated with a modified Crosstool-NG version).

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

toolchain/Config.in

@@ -10,7 +10,7 @@ choice
 
 config BR2_TOOLCHAIN_BUILDROOT
 	bool "Buildroot toolchain"
-	depends on !BR2_microblaze
+	depends on !BR2_microblaze && !BR2_aarch64
 	select BR2_TOOLCHAIN_HAS_SHADOW_PASSWORDS
 	select BR2_TOOLCHAIN_HAS_THREADS_DEBUG_IF_NEEDED
 
@@ -23,7 +23,7 @@ config BR2_TOOLCHAIN_EXTERNAL
 
 config BR2_TOOLCHAIN_CTNG
 	bool "Crosstool-NG toolchain"
-	depends on !BR2_microblaze
+	depends on !BR2_microblaze && !BR2_aarch64
 	select BR2_TOOLCHAIN_HAS_SHADOW_PASSWORDS
 	select BR2_TOOLCHAIN_HAS_THREADS_DEBUG_IF_NEEDED
 	help