[yocto] Add extra parameters for qemu script

[Ke, Liping]

Hi, Scott

The patch is in the attachment for your review. Below is some notes:

1) Basically I wouldn't like to change any logic of the original code.
2) -serial stdio and -nographic options are removed since they're be covered by the extra parameters.
3) User input would be $poky-qemu qemux86 "<-nographic -m 300>"
4) -m input will be checked still. If it exceeds 128 for arm, it will be changed back to
   128M, same logic as before. And after parsing, -m option will be removed and replaced by
    Kernel options mem=128M for avoiding some instability issue.

Generally I modified very few, just add an extra parameters with least intrusion of
Current logic.

Any comments are welcomed. 
I will conduct more test with latest code in parallel.

Thanks a lot for your help!
 criping
-------------- next part --------------
A non-text attachment was scrubbed...
Name: qemu_extra_options.patch
Type: application/octet-stream
Size: 3652 bytes
Desc: qemu_extra_options.patch
URL: <http://lists.yoctoproject.org/pipermail/yocto/attachments/20101209/5e6bcad2/attachment.obj>