tty: Remove redundant synclinkmp driver

tty: Remove redundant synclinkmp driver

A note from the vendor:

 "The hardware used with synclink.c and synclinkmp.c has not been
  manufactured for 15 years and was low volume. The chances of either
  driver still being in use is very low. Not even Microgate (me) has
  the ability to test either anymore (no hardware). I don’t know the
  policy about driver removal, but I think both could be removed
  without upsetting anyone."

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201105123357.708813-3-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>