modetest: push pipe_resolve_connectors() to set_mode

The function is closely related to pipe_find_crtc_and_mode() so we might
as well keep them together.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Ezequiel Garcia <ezequiel@collabora.com>
Tested-by: Ezequiel Garcia <ezequiel@collabora.com>