shadow-securetty: add ttyAM[0-3] serial ports

shadow-securetty: add ttyAM[0-3] serial ports

Old version of the ARM AMBA serial port driver creates those device nodes.

(From OE-Core rev: fa17b9ea435f5c49e3bea56524152b21d915d464)

(From OE-Core rev: 0956df1596f899337afb3551db01a59bf1c38856)

Signed-off-by: Javier Viguera <javier.viguera@digi.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>