serial8250: Add dl_read()/dl_write() callbacks

Convert serial_dl_read() and serial_dl_write() from macro
to 8250 specific callbacks. This change makes it easier to
support 8250 hardware with non-standard DLL and DLM register
configurations such as Alchemy, RM9K and upcoming Emma Mobile
UART hardware.

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250.h

@@ -37,6 +37,10 @@ struct uart_8250_port {
 	unsigned char		lsr_saved_flags;
 #define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA
 	unsigned char		msr_saved_flags;
+
+	/* 8250 specific callbacks */
+	int			(*dl_read)(struct uart_8250_port *);
+	void			(*dl_write)(struct uart_8250_port *, int);
 };
 
 struct old_serial_port {
@@ -98,6 +102,16 @@ static inline void serial_out(struct uart_8250_port *up, int offset, int value)
 
 void serial8250_clear_and_reinit_fifos(struct uart_8250_port *p);
 
+static inline int serial_dl_read(struct uart_8250_port *up)
+{
+	return up->dl_read(up);
+}
+
+static inline void serial_dl_write(struct uart_8250_port *up, int value)
+{
+	up->dl_write(up, value);
+}
+
 #if defined(__alpha__) && !defined(CONFIG_PCI)
 /*
  * Digital did something really horribly wrong with the OUT1 and OUT2