serial: 8250: don't use slave_id of dma_slave_config

That field has been deprecated in favour of getting the necessary information
from ACPI or DT.

However, we still need to deal systems that are PCI only (no ACPI to back up)
like Intel Bay Trail. In order to support such systems, we explicitly bind
setup() to the appropriate DMA filter function and its corresponding parameter.
Then when serial8250_request_dma() doesn't find the channel via ACPI or DT, it
falls back to use the given filter function.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>