uboot-phytec

buildman: Allow the toolchain priority to be specified

At present the priority of a toolchain is calculated from its filename based
on hard-coded rules. Allow it to be specified by the caller. We will use
this in a later patch. Also display the priority and provide a message when
it is overriden by another toolchain of higher priority.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>