cpuidle: qcom-spm: Check if any CPU is managed by SPM

At the moment, the "qcom-spm-cpuidle" platform device is always created,
even if none of the CPUs is actually managed by the SPM. On non-qcom
platforms this will result in infinite probe-deferral due to the
failing qcom_scm_is_available() call.

To avoid this, look through the CPU DT nodes and check if there is
actually any CPU managed by a SPM (as indicated by the qcom,saw property).
It should also be available because e.g. MSM8916 has qcom,saw defined
but it's typically not enabled with ARM64/PSCI firmwares.

This is needed in preparation of a follow-up change that calls
qcom_scm_set_warm_boot_addr() a single time before registering any
cpuidle drivers. Otherwise this call might be made even on devices
that have this driver enabled but actually make use of PSCI.

Fixes: 60f3692b5f0b ("cpuidle: qcom_spm: Detach state machine from main SPM handling")
Reported-by: Marek Szyprowski <[email protected]>
Link: https://lore.kernel.org/r/[email protected]/
Signed-off-by: Stephan Gerhold <[email protected]>
Tested-by: Marek Szyprowski <[email protected]>
Acked-by: Daniel Lezcano <[email protected]>
Signed-off-by: Bjorn Andersson <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

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