ACPI: scan: Simplify acpi_table_events_fn()

Notice that the table field of struct acpi_table_events_work is never
read and its event field is always equal to ACPI_TABLE_EVENT_LOAD, so
both of them are redundant.

Accordingly, drop struct acpi_table_events_work and use struct
work_struct directly instead of it, simplify acpi_scan_table_handler()
and rename it to acpi_scan_table_notify().

Moreover, make acpi_bus_table_handler() check the event code against
ACPI_TABLE_EVENT_LOAD before calling acpi_scan_table_notify(), so it
is not necessary to do that check in the latter.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>