staging: unisys: visorbus: Replace two base postcode macros with one

Leverage the 3 existing s-Par postcode macros to do a bit more work
and provide only 1 base postcode macro.

Signed-off-by: Bryan Thompson <bryan.thompson@unisys.com>
Signed-off-by: David Kershner <david.kershner@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>