PCI: brcmstb: Use bridge reset if available

PCI: brcmstb: Use bridge reset if available

The 7712 SoC has a bridge reset which can be described in the device
tree.

Use it if present.  Otherwise, continue to use the legacy method to
reset the bridge.

Link: https://lore.kernel.org/linux-pci/20240815225731.40276-6-james.quinlan@broadcom.com
Signed-off-by: Jim Quinlan <james.quinlan@broadcom.com>
[kwilczynski: commit log, refactored function brcm_pcie_bridge_sw_init_set_generic()]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Stanimir Varbanov <svarbanov@suse.de>