ACPI: CPPC: Accept requests to retain immutable autonomous selection

ACPI permits Autonomous Selection Enable to be Integer 1 when the platform
always selects performance autonomously. cppc_get_auto_sel() returns that
value, but cppc_set_auto_sel() rejects the Integer even when asked to keep
autonomous selection enabled. AMD shared-memory initialization consequently
fails in active or guided mode after successfully reading the capability.

Accept a request to keep this immutable field enabled without issuing a
register access. Expose the immutable encoding to callers, separately from
the current value of a writable register.

Before an AMD shared-memory transition to passive mode, reject immutable
autonomous selection on any present CPU. Otherwise a guided-to-passive
transition ignores the failed disable and reports the wrong mode, while
active-to-passive unregisters the working driver before passive policy
initialization fails. Check under the driver mode lock before invoking
either transition, including known offline CPUs.

Serialize this capability query with descriptor publication and removal.
ACPI processor removal drops the descriptor before taking the CPU hotplug
write lock, so the caller's cpus_read_lock() alone cannot protect the
lookup. Unpublish under the same mutex before releasing a descriptor,
including when adding its kobject fails.

The cppc-cpufreq auto_select attribute can also request one while
autonomous selection is already enabled. If the subsequent bounds update
fails, its rollback requests zero and clears the cached mode regardless
of the previous state. For an immutable field the disable request fails,
leaving the cached mode wrong. Save and restore the previous mode instead.
This also avoids disabling an already-enabled writable control on that
error path.

Fixes: c984f5d5d45b ("ACPI: CPPC: Add auto select register read/write support")
Fixes: ea3db45ae476 ("cpufreq: cppc: Update MIN_PERF/MAX_PERF in target callbacks")
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Sumit Gupta <sumitg@nvidia.com>
Link: https://patch.msgid.link/20260916162805.1039247-19-christian.loehle@arm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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