core: don't flush the serial port queue for a serial command

core: don't flush the serial port queue for a serial command

Don't flush the serial port queue when encountering a "serial"
command.  We don't actually want to lose data due to a repeated
"serial", since it's quite likely it's exactly the same as before.

Do flush the queue on hardware cleanup, however.

Also fix some minor bugs, including a bunch of code in the .data
segment.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>