PCI: rockchip-ep: Refactor rockchip_pcie_ep_probe() memory allocations

Introduce the function rockchip_pcie_ep_init_ob_mem() allocate the
outbound memory regions and memory needed for IRQ handling.

These changes tidy up rockchip_pcie_ep_probe().

No functional change.

Link: https://lore.kernel.org/r/20241017015849.190271-9-dlemoal@kernel.org


Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>