uboot-imx

buildman: Drop the toolchain error when downloading toolchains

It doesn't make sense to complain about missing toolchains when the
--fetch-arch option is being used. The user is presumably aware that there
is a toolchain problem and is actively correcting it by running with this
option.

Refactor the code to avoid printing this confusing message.

Signed-off-by: Simon Glass <sjg@chromium.org>