ACPI / scan: Start matching drivers after trying scan handlers

ACPI scan handlers should always be attached to struct acpi_device
objects before any ACPI drivers, but there is a window during which
a driver may be attached to a struct acpi_device before checking if
there is a matching scan handler.  Namely, that will happen if an
ACPI driver module is loaded during acpi_bus_scan() right after
the first namespace walk is complete and before the given device
is processed by the second namespace walk.

To prevent that from happening, set the match_driver flags of
struct acpi_device objects right before running device_attach()
for them in acpi_bus_device_attach().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>