firmware: stratix10-svc: add PSCI secondary CPU offline on warm reboot for agilex and stratix10

On Agilex7 and Stratix10 SoCs, secondary CPUs must be offlined before
a warm reboot to ensure a clean PSCI state. Agilex5 warm reset is a
SDM-owned HPS reset that holds secondaries in the new reset-release until
ATF releases them, so the secondary cores dont have to be put offline
first. Register a reboot notifier that calls remove_cpu() on each
secondary CPU when SYS_RESTART is triggered in REBOOT_WARM mode.

A snapshot of cpu_online_mask is taken before the loop since remove_cpu()
modifies the mask as CPUs go down. CPU 0 is excluded as it is typically
not hotpluggable. Failures are logged and the loop continues so the
reboot is not blocked by a single CPU that refuses to offline.
The of_device_id table carries a per-compatible pdata flag to enable the
notifier only on platforms that need it; Agilex5 leaves the flag unset.

The notifier is unregistered at the start of remove(), before async
channel teardown, to prevent a reboot notification from racing with
driver shutdown.

Signed-off-by: Adrian Ng Ho Yin <adrian.ho.yin.ng@altera.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>

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