tty: bfin, define inlined structures

struct bfin_serial_port contains structs circ_buf, timer_list, and
work_struct directly (not pointers). This means that these structures
have to be defined completely to be inlined in struct
bfin_serial_port.

So instead of struct declarations, define the structures by including
proper headers. They were pulled in by linux/serial_core.h or others
until now. But experimenting with circ_buf removal from serial_core,
struct circ_buf becomes undefined in bfin_serial:

In file included from arch/blackfin/kernel/debug-mmrs.c:21:0:
arch/blackfin/include/asm/bfin_serial.h:44:18: error: field 'rx_dma_buf' has incomplete type
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/blackfin/include/asm/bfin_serial.h

@@ -9,8 +9,11 @@
 #ifndef __BFIN_ASM_SERIAL_H__
 #define __BFIN_ASM_SERIAL_H__
 
+#include <linux/circ_buf.h>
 #include <linux/serial_core.h>
 #include <linux/spinlock.h>
+#include <linux/timer.h>
+#include <linux/workqueue.h>
 #include <mach/anomaly.h>
 #include <mach/bfin_serial.h>
 
@@ -25,10 +28,6 @@
 # endif
 #endif
 
-struct circ_buf;
-struct timer_list;
-struct work_struct;
-
 struct bfin_serial_port {
 	struct uart_port port;
 	unsigned int old_status;