dm: serial: Introduce ->getinfo() callback

New callback will give a necessary information to fill up ACPI SPCR table,
for example. Maybe used later for other purposes.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Change ADR_SPACE_SYSTEM_IO to SERIAL_ADDRESS_SPACE_IO to fix build error:
Signed-off-by: Simon Glass <sjg@chromium.org>