RFC: moveconfig: Use toolchains from buildman

It is annoying to have to set up and maintain two sets of toolchains, one
for buildman and one for moveconfig.

Adjust moveconfig to make use to buildman's toolchains. This should make
things easier.

One missing feature is the ability to specify the toolchain on the command
line with a special environment variable, e.g. CROSS_COMPILE_ARM. I'm not
sure if that is useful, but if it is it could be implemented in buildman.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Tested-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>