bus: brcmstb_gisb: Add register offset tables for older chips

This will select the appropriate register layout based on the DT
"compatible" string.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

diff --cc Documentation/devicetree/bindings/bus/brcm,gisb-arb.txt
Simple merge

diff --cc drivers/bus/brcmstb_gisb.c
Simple merge