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

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

commit 9e9ec8d8692a6f64d81ef67d4fb6255af6be684b upstream.

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 15b23906347c ("PCI: dwc: Add link up check in dw_child_pcie_ops.map_bus()").

Fixes: 10a797c6e54a ("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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>