serial: 8250_dw: Let ACPI code extract the DMA client info

The new ACPI DMA helpers in dmaengine API can take care of
extracting all the necessary information regarding DMA. The
driver does not need to do this separately any more.

Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>