PCI: dw-rockchip: Use rockchip_pcie_link_up() to check link up instead of open coding

Some of the callers of rockchip_pcie_link_up() are open coding the
rockchip_pcie_link_up() function, leading to code duplication. So switch
them to use rockchip_pcie_link_up() function.

Also, use the FIELD_GET() macro to simplify the link up check in
rockchip_pcie_link_up().

Signed-off-by: Hans Zhang <18255117159@163.com>
[mani: subject and description rewording]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://patch.msgid.link/20250427125316.99627-4-18255117159@163.com