PM: domains: Extend dev_pm_domain_detach() doc

Mention all domain attach menthods which dev_pm_domain_detach()
reverses.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>