staging: unisys: include: Remove unneeded includes from visorbus.h

A bunch of code churn has caused the following include files to not be
needed by visorbus.h:

linux/poll.h
linux/kernel.h
linux/uuid.h
linux/seq_file.h

Reviewed-by: Sameer Wadgaonkar <sameer.wadgaonkar@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>