PM: domains: Fix domain attach for CONFIG_PM_OPP=n

If CONFIG_PM_OPP=n, of_get_required_opp_performance_state() always
returns -EOPNOTSUPP, and all drivers for devices that are part of a PM
Domain fail to probe with:

    failed to set required performance state for power-domain foo: -95
    probe of bar failed with error -95

Fix this by treating -EOPNOTSUPP the same as -ENODEV.

Fixes: c016baf7 ("PM: domains: Add support for 'required-opps' to set default perf state")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>