showing a splash picture when start

showing a splash picture when start

    Added options to let qemu transfer two configuration files to bios:
"bootsplash.bmp" and "etc/boot-menu-wait", which could be specified by command
    -boot splash=P,splash-time=T
P is jpg/bmp file name or an absolute path, T have a max value of 0xffff, unit
is ms. With these two options, if user invoke qemu with menu=on option, then
a splash picture would be showed in a given time. For example:
    qemu -boot menu=on,splash=/root/boot.bmp,splash-time=5000
would make boot.bmp shown as a brand with 5 seconds in the booting up process.
This feature need the new seabios's support, which could be got from git.

Signed-off-by: Wayne Xia <[email protected]>
Signed-off-by: Anthony Liguori <[email protected]>