Add search path support for qemu data files.

This patch allows to specify multiple directories where qemu should look
for data files.  To implement that the behavior of the -L switch is
slightly different now:  Instead of replacing the data directory the
path specified will be appended to the data directory list.  So when
specifiying -L multiple times all directories specified will be checked,
in the order they are specified on the command line, instead of just the
last one.

Additionally the default paths are always appended to the directory
data list.  This allows to specify a incomplete directory (such as the
seabios out/ directory) via -L.  Anything not found there will be loaded
from the default paths, so you don't have to create a symlink farm for
all the rom blobs.

For trouble-shooting a tracepoint has been added, logging which blob
has been loaded from which location.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1362739344-8068-1-git-send-email-kraxel@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
