PCI: j721e: Add per platform maximum lane settings

PCI: j721e: Add per platform maximum lane settings

Various platforms have different maximum amount of lanes that can be
selected. Add max_lanes to struct j721e_pcie to allow for detection of this
which is needed to calculate the needed bitmask size for the possible lane
count.

Link: https://lore.kernel.org/linux-pci/20231128054402.2155183-4-s-vadapalli@ti.com
Signed-off-by: Matt Ranostay <mranostay@ti.com>
Signed-off-by: Achal Verma <a-verma1@ti.com>
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Ravi Gunasekaran <r-gunasekaran@ti.com>