tty: add a DesignWare 8250 driver

The Synopsys DesignWare 8250 is an 8250 that has an extra interrupt that
gets raised when writing to the LCR when busy.  To handle this we need
special serial_out, serial_in and handle_irq methods.  Add a new
platform driver that uses these accessors.

Cc: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 10babe2..8ee3a66 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -267,6 +267,13 @@
 	  port hardware found on MIPS RM9122 and similar processors.
 	  If unsure, say N.
 
+config SERIAL_8250_DW
+	tristate "Support for Synopsys DesignWare 8250 quirks"
+	depends on SERIAL_8250 && OF
+	help
+	  Selecting this option will enable handling of the extra features
+	  present in the Synopsys DesignWare APB UART.
+
 comment "Non-8250 serial port support"
 
 config SERIAL_AMBA_PL010