uboot-imx

dm: serial: ns16550: Update to support of-platdata

With of-platdata this driver cannot know the format of the of-platdata
struct, so we cannot use generic code for accessing the of-platdata. Each
SoC that uses this driver will need to set up ns16550's platdata for it.
So don't compile in the generic code.

Signed-off-by: Simon Glass <sjg@chromium.org>