Serial-uclass should be generically implemented without depending
a particular hardware. Fortunately, nothing in include/ns16550.h is
referenced from drivers/serial/serial-uclass.c, so remove this bogus
include.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Reviewed-by: Tom Rini <trini@konsulko.com> Acked-by: Simon Glass <sjg@chromium.org>