serial: move struct uart_8250_port from 8250.c to 8250.h

Since we want to promote sharing and move away from one single
uart driver with a bunch of platform specific bugfixes all
munged into one, relocate some header like material from
the C file to the header.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>