PCI: brcmstb: Set bus max burst size by chip type

The proper value of the parameter SCB_MAX_BURST_SIZE varies per chip.  The
2711 family requires 128B whereas other devices can employ 512.  The
assignment is complicated by the fact that the values for this two-bit
field have different meanings;

  Value   Type_Generic    Type_7278

     00       Reserved         128B
     01           128B         256B
     10           256B         512B
     11           512B     Reserved

Link: https://lore.kernel.org/r/20200911175232.19016-10-james.quinlan@broadcom.com


Signed-off-by: Jim Quinlan <jquinlan@broadcom.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>