Possible runqemu release note for Nanbield

[Mark Hatle <mark.hatle@kernel.crashing.org>]

While porting meta-xilinx to nanbield I ran into a difference with the way 
runqemu works.  I figure this might be something that should be a release note, 
but unfortunately I'm not sure I understand how to explain it well.  Below are 
my findings and maybe we can word-smith this into a proper release note.

In Mickledore and before 'runqemu' when run like:

runqemu nographic

would automatically add "-serial mon:stdio" after the QB_OPT_APPEND values as 
necessary.  (It might have also added "-serial null" in some cases, but after 
"-serial mon:stdio".). After the commit:

https://git.yoctoproject.org/poky/commit/?h=nanbield&id=8c4bb95c1c472f9eb5235b848e57febcac53aa59

This has changed to counting the number of serial ports and adding "-serial 
null" if the QB_OPT_APPEND only defined a single serial port, and if two or more 
ports are specified avoiding automatically adding -serial mon:stdio.  This can 
break some existing QEMU based configurations by changing the way the serial 
ports are automatically determined when runqemu is executed.

It may be necessary to compare a prior working (Mickledore) executing and 
adjusting QB_OPT_APPEND to include the correct ordering and number of serial 
ports of the emulated machine.



Hopefully Richard or someone can verify what I wrong about is accurate, and 
maybe adjust it to better explain how a user should adjust their BSP integration.

Thanks!

--Mark