arm64: acpi: Make apei_claim_sea() synchronise with APEI's irq work

APEI is unable to do all of its error handling work in nmi-context, so
it defers non-fatal work onto the irq_work queue. arch_irq_work_raise()
sends an IPI to the calling cpu, but we can't guarantee this will be
taken before we return.

Unless we interrupted a context with irqs-masked, we can call
irq_work_run() to do the work now. Otherwise return -EINPROGRESS to
indicate ghes_notify_sea() found some work to do, but it hasn't
finished yet.

With this we can take apei_claim_sea() returning '0' to mean this
external-abort was also notification of a firmware-first RAS error,
and that APEI has processed the CPER records.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Punit Agrawal <punit.agrawal@arm.com>
Tested-by: Tyler Baicar <tbaicar@codeaurora.org>
CC: Xie XiuQi <xiexiuqi@huawei.com>
CC: gengdongjiu <gengdongjiu@huawei.com>
---
Changes since v2:
 * Removed IS_ENABLED() check, done by the caller unless we have a dummy
   definition.