kgdb: remove #include <linux/serial_8250.h> from kgdb.h

There's no reason kgdb.h itself needs to include the 8250 serial port
header file.  So push it down to the _very_ limited number of individual
drivers that need the values in that file, and fix up the places where
people really wanted serial_core.h and platform_device.h.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/kgdb_nmi.c

@@ -23,6 +23,7 @@
 #include <linux/tty.h>
 #include <linux/tty_driver.h>
 #include <linux/tty_flip.h>
+#include <linux/serial_core.h>
 #include <linux/interrupt.h>
 #include <linux/hrtimer.h>
 #include <linux/tick.h>