ARM: cpuidle: Remove overzealous error logging

CPUidle back-end operations are not implemented in some platforms
but this should not be considered an error serious enough to be
logged. Check the arm_cpuidle_init() return value to detect whether
the failure must be reported or not in the kernel log and do
not log it if the platform does not support CPUidle operations.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Signed-off-by: Will Deacon <will@kernel.org>