staging: unisys: Move vbushelper.h to visorbus directory

Only visorbus needs this header file so move it to visorbus
directory.

Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Tim Sell <Timothy.Sell@unisys.com>
Acked-By: Neil Horman <nhorman@tuxdriver.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>