PCI: brcmstb: Expand inbound window size up to 64GB

The BCM2712 memory map can support up to 64GB of system memory, thus
expand the inbound window size in calculation helper function.

The change is safe for the currently supported SoCs that have smaller
inbound window sizes.

Signed-off-by: Stanimir Varbanov <svarbanov@suse.de>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Jim Quinlan <james.quinlan@broadcom.com>
Tested-by: Ivan T. Ivanov <iivanov@suse.de>
Link: https://lore.kernel.org/r/20250224083559.47645-7-svarbanov@suse.de


[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>