PCI: brcmstb: Set RCB_{MPS,64B}_MODE bits

Set RCB_MPS mode bit so that data for PCIe read requests up to the size of
the Maximum Payload Size (MPS) are returned in one completion, and data for
PCIe read requests greater than the MPS are split at the specified Read
Completion Boundary setting.

Set RCB_64B so that the Read Compeletion Boundary is 64B.

Link: https://lore.kernel.org/r/20221011184211.18128-6-jim2101024@gmail.com


Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>