cpuidle: psci: Fail cpuidle registration if set OSI mode failed

Currently we allow the cpuidle driver registration to succeed, even if we
failed to enable the OSI mode when the hierarchical DT layout is used. This
means running in a degraded mode, by using the available idle states per
CPU, while also preventing the domain idle states.

Moving forward, this behaviour looks quite questionable to maintain, as
complexity seems to grow around it, especially when trying to add support
for deferred probe, for example.

Therefore, let's make the cpuidle driver registration to fail in this
situation, thus relying on the default architectural cpuidle backend for
WFI to be used.

Reviewed-by: Lina Iyer <ilina@codeaurora.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>