runqueue: Add support for <task>- syntax

runqueue: Add support for <task>- syntax

It can be useful to run all tasks up to but not including a specific task. The
main reason this was never added was the lack of a good syntax. This patch
uses the syntax <taskname>- to denote this behaviour which is simple, not
invasive and fits what we need from good syntax IMO, hence we can add this.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>