Add conflicts in module-build-macros for NEVRAs found in handle_collisions_with_base_module_rpms
    
    PR #1331 made the assumption that the Ursa Major ursine RPMs were at
    xmd["mbs"]["ursine_rpms"], but they are actually at
    xmd["mbs"]["buildrequires"]["platform"]["ursine_rpms"]. This commit
    handles the ursine RPMs generated by handle_collisions_with_base_module_rpms
    separately since the base module the RPMs came from are not tracked in
    that function.