staging: unisys: visorhba: simplify and enhance debugfs interface

debugfs info for each visorhba device is now presented by a file named of
the following form within the debugfs tree:

    visorhba/vbus<x>:dev<y>/info

where <x> is the vbus number, and <y> is the relative device number.

Also, the debugfs presentation function was converted to use the seq_file
interface, so that it could access the device context without resorting to
a global array.  This also simplified the function.

Signed-off-by: Tim Sell <Timothy.Sell@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>