tty: n_smux: Add SMUX TTY Line Discipline Driver

Add new Serial Multiplexer (SMUX) driver.

This driver multiplexes multiple logical channels over a single
physical HSUART channel using the TTY Line Discipline framework.
This driver will be used in Fusion 4 for control plane, data plane
and DIAG traffic between Application processor and QSC modem.

Change-Id: Ibecf6cea872f5baf11fb93ded6124243a37a2085
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>
Signed-off-by: Angshuman Sarkar <angshuman@codeaurora.org>
Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 1ff6b62..818d189 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -52,6 +52,7 @@
 #define N_TI_WL		22	/* for TI's WL BT, FM, GPS combo chips */
 #define N_TRACESINK	23	/* Trace data routing for MIPI P1149.7 */
 #define N_TRACEROUTER	24	/* Trace data routing for MIPI P1149.7 */
+#define N_SMUX		25	/* Serial MUX */
 
 /*
  * This character is the same as _POSIX_VDISABLE: it cannot be used as