tty: smux_ctl: close SMUX port during SSR

If a subsystem restart occurs, the SMUX port needs to be closed when the
platform device is removed and then re-opened when the platform device
is probed again.  Without this functionality, the SMUX port state is not
properly reset resulting in a data stall.

Add code to close the SMUX port when the platform device is removed.

CRs-Fixed: 474388
Change-Id: I00039fa517a5cf6b4d9230114cac7c6c9bbba9d1
Signed-off-by: Eric Holmberg <eholmber@codeaurora.org>