8250.c: support specifying DW APB UARTs in device platform_data

Allow the private_data field to be specified in platform_data for the
standard 8250/16550 UART.  This field is used by DW APB type UARTs and
without this patch it's only possible to set this field when registering
the port by hand.  If private_data is not set then the driver will
potentially oops with a NULL pointer dereference.

Signed-off-by: Will Newton <will.newton@gmail.com>
Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/serial_8250.h

@@ -23,6 +23,7 @@ struct plat_serial8250_port {
 	resource_size_t	mapbase;	/* resource base */
 	unsigned int	irq;		/* interrupt number */
 	unsigned int	uartclk;	/* UART clock rate */
+	void            *private_data;
 	unsigned char	regshift;	/* register shift */
 	unsigned char	iotype;		/* UPIO_* */
 	unsigned char	hub6;