Refactor and comment downloaded and compiled toolchains

Move the common parts of br-ext/configs/toolchain-aarch32-sdk and
br-ext/configs/toolchain-aarch64-sdk into
br-ext/configs/toolchain-common-sdk.
br-ext/configs/toolchain-aarch32-sdk was previously using
BR2_TOOLCHAIN_EXTERNAL_GCC_11=y and is now by using
br-ext/configs/toolchain-common-sdk updated to use the correct
BR2_TOOLCHAIN_EXTERNAL_GCC_14=y.

Add comments where to update if compiled or downloaded toolchain is
updated.

Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
diff --git a/common.mk b/common.mk
index 573641f..6e37667 100644
--- a/common.mk
+++ b/common.mk
@@ -258,12 +258,12 @@
 endif
 else ifeq ($(UNAME_M),aarch64)
 ifeq ($(COMPILE_NS_USER),64)
-BUILDROOT_TOOLCHAIN=toolchain-aarch64-sdk
+BUILDROOT_TOOLCHAIN=toolchain-aarch64-sdk toolchain-common-sdk
 else
 BUILDROOT_TOOLCHAIN=toolchain-aarch32
 endif
 else
-BUILDROOT_TOOLCHAIN=toolchain-aarch$(COMPILE_NS_USER)-sdk
+BUILDROOT_TOOLCHAIN=toolchain-aarch$(COMPILE_NS_USER)-sdk toolchain-common-sdk
 endif
 endif
 
@@ -344,7 +344,8 @@
 		--top-dir "$(ROOT)" \
 		--br-defconfig build/br-ext/configs/optee_$(BUILDROOT_ARCH) \
 		--br-defconfig build/br-ext/configs/optee_generic \
-		--br-defconfig build/br-ext/configs/$(BUILDROOT_TOOLCHAIN) \
+		$(addprefix --br-defconfig build/br-ext/configs/, \
+			    $(BUILDROOT_TOOLCHAIN)) \
 		$(DEFCONFIG_GDBSERVER) \
 		$(DEFCONFIG_XEN) \
 		$(DEFCONFIG_TSS) \