PCI: keystone: Add link up check to ks_pcie_other_map_bus()

K2G forwards the error triggered by a link-down state (e.g., no connected
endpoint device) on the system bus for PCI configuration transactions;
these errors are reported as an SError at system level, which is fatal and
hangs the system.

So, apply fix similar to how it was done in the DesignWare Core driver
commit 15b23906 ("PCI: dwc: Add link up check in dw_child_pcie_ops.map_bus()").

Fixes: 10a797c6 ("PCI: dwc: keystone: Use pci_ops for config space accessors")
Link: https://lore.kernel.org/r/20240524105714.191642-3-s-vadapalli@ti.com


Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
[kwilczynski: commit log, added tag for stable releases]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Cc: stable@vger.kernel.org