dim: allow a space separated list of URLs for each repo in drm_tip_repos

This lets us configure a space separated list of URLs for each repo in
drm_tip_repos, with all accepted protocols and sources, and the first
one found gets picked. This way we don't have to have a complicated set
of rules for converting between ssh, git and https protocol URLs.

Acked-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>