sysvinit-inittab_2.88dsf.bb: Allow multiple serial port consoles to be defined

sysvinit-inittab_2.88dsf.bb: Allow multiple serial port consoles to be defined

Set SERIAL_CONSOLES if you want to define multiple serial consoles, also if
you need to check for the presence of the serial consoles you can also define
SERIAL_CONSOLES_CHECK to determine if these are present when you boot. This
will prevent error message that pop up when the serial port is not present.

SERIAL_CONSOLES = "115200;ttyS0 115200;ttyS1 115200;ttyEHV0"
SERIAL_CONSOLES_CHECK = "${SERIAL_CONSOLES}"

The above lines in machine.conf or elsewhere will have the effect of having
two serial consoles and removing any that are not present at boot

Signed-off-by: Saul Wold <sgw@linux.intel.com>