PCI: aspeed: Add ASPEED PCIe RC driver

PCI: aspeed: Add ASPEED PCIe RC driver

Introduce PCIe Root Complex driver for ASPEED SoCs. Support RC
initialization, reset, clock, IRQ domain, and MSI domain setup. Implement
platform-specific setup and register configuration for ASPEED. And provide
PCI config space read/write and INTx/MSI interrupt handling.

Signed-off-by: Jacky Chou <jacky_chou@aspeedtech.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20251216-upstream_pcie_rc-v7-6-4aeb0f53c4ce@aspeedtech.com