serial: Support the EFR-register of XR1715x uarts.

The EFR (Enhenced-Features-Register) is located at a different offset
than the other devices supporting UART_CAP_EFR. This change add a special
setup quick to set UPF_EXAR_EFR on the port. UPF_EXAR_EFR is then used to
the port type to PORT_XR17D15X since it is for sure a XR17D15X uart.

Signed-off-by: Søren Holm <sgh@sgh.dk>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/include/linux/serial_reg.h b/include/linux/serial_reg.h
index c75bda3..8ce70d7 100644
--- a/include/linux/serial_reg.h
+++ b/include/linux/serial_reg.h
@@ -152,6 +152,7 @@
  * LCR=0xBF (or DLAB=1 for 16C660)
  */
 #define UART_EFR	2	/* I/O: Extended Features Register */
+#define UART_XR_EFR	9	/* I/O: Extended Features Register (XR17D15x) */
 #define UART_EFR_CTS		0x80 /* CTS flow control */
 #define UART_EFR_RTS		0x40 /* RTS flow control */
 #define UART_EFR_SCD		0x20 /* Special character detect */