PCI: amd-mdb: Add support for PCIe RP PERST# signal handling

PCI: amd-mdb: Add support for PCIe RP PERST# signal handling

Add support for handling the AMD Versal Gen 2 MDB PCIe Root Port PERST#
signal via a GPIO by parsing the new PCIe bridge node to acquire the
reset GPIO. If the bridge node is not found, fall back to acquiring it
from the PCIe host bridge node.

As part of this, update the interrupt controller node parsing to use
of_get_child_by_name() instead of of_get_next_child(), since the PCIe
host bridge node now has multiple children. This ensures the correct
node is selected during initialization.

Signed-off-by: Sai Krishna Musham <sai.krishna.musham@amd.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20250807074019.811672-3-sai.krishna.musham@amd.com