In order to remove the additional check before calling the
ghes_notify_sea(), make stub definition when !CONFIG_ACPI_APEI_SEA.

After this cleanup, we can simply call the ghes_notify_sea() to let
APEI driver handle the SEA notification.
Signed-off-by: NDongjiu Geng <gengdongjiu@huawei.com>
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>