staging: gasket: TODO: re-implement using UIO

The gasket in-kernel framework, recently introduced under staging,
re-implements what is already long-time provided by the UIO
subsystem, with extra PCI BAR remapping and MSI conveniences.

Before moving it out of staging, make sure we add the new bits to
the UIO framework instead, then transform its signle client, the
Apex driver, to a proper UIO driver (uio_driver.h).

Link: https://lkml.kernel.org/r/20180828103817.GB1397@do-kernel



Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>