[Libdlo] Tips for setting up displaylink with Xinerama

[Bernie Thompson]

Hi Doug and Christoph,

Thanks for fleshing these build dependencies out.  Here are some
changes to help the next people doing it.

For the sys and defio dependencies, the udlfb code at git.plugable.com
has been updated to better capture the dependencies in Kconfig -- this
should make everything "just work" for those building the code from
within the kernel tree. - e.g.

make M=drivers/staging/udlfb

from the top of the linux kernel tree, once you've updated the udlfb files.

And for those building the module separately outside of the kernel
build, the Makefile will now print out a hint with the typical build
errors you'll see when the kernel doesn't have the right support, and
what to enable.

Please report back if you find any problems with this, particularly the Kconfig.

Note if you're running Robertos "displaylink" X server (not fbdev),
then you don't necessarily need this bleeding-edge udlfb from
git.plugable.com -- earlier versions will likely work fine for you.
But the testing and bug reports are welcome anyway, as it helps speed
up when that codeline is ready to be bundled into patches for the
kernel tree.

Thanks,
Bernie