Let's avoid some of the boilerplate code to manage the various PM domain
cases, by converting into using dev_pm_domain_attach|detach_list().

As a part of the conversion, we are moving over to use device_links, which
simplifies the runtime PM support too. Moreover, while attaching let's
trust that an already attached single PM domain is the correct one.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Bjorn Andersson <andersson@kernel.org>
Cc: Konrad Dybcio <konrad.dybcio@linaro.org>
Cc: <linux-remoteproc@vger.kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://lore.kernel.org/r/20240130123951.236243-5-ulf.hansson@linaro.org