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> Signed-off-by: David Brown <davidb@codeaurora.org>