ACPI / APEI: Switch NOTIFY_SEA to use the estatus queue

Now that the estatus queue can be used by more than one notification
method, we can move notifications that have NMI-like behaviour over.

Switch NOTIFY_SEA over to use the estatus queue. This makes it behave
in the same way as x86's NOTIFY_NMI.

Remove Kconfig's ability to turn ACPI_APEI_SEA off if ACPI_APEI_GHES
is selected. This roughly matches the x86 NOTIFY_NMI behaviour, and means
each architecture has at least one user of the estatus-queue, meaning it
doesn't need guarding with ifdef.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>