hw/pci-host/aspeed: Add AST2600 PCIe config space and host bridge

Introduce PCIe config and host bridge model for the AST2600 platform.

This patch adds support for the H2X (AHB to PCIe Bus Bridge) controller
with a 0x100 byte register space. The register layout is shared between
two root complexes: 0x00–0x7f is common, 0x80–0xbf for RC_L, and 0xc0–0xff
for RC_H. Only RC_H is modeled in this implementation.

The RC_H bus uses bus numbers in the 0x80–0xff range instead of the
standard root bus 0x00. To allow the PCI subsystem to discover devices,
the host bridge logic remaps the root bus number back to 0x00 whenever the
configured bus number matches the "bus-nr" property.

New MMIO callbacks are added for the H2X config space:
- aspeed_pcie_cfg_read() and aspeed_pcie_cfg_write() handle register
  accesses.
- aspeed_pcie_cfg_readwrite() provides configuration read/write support.
- aspeed_pcie_cfg_translate_write() handles PCIe byte-enable semantics for
  write operations.

The reset handler initializes the H2X register block with default values
as defined in the AST2600 datasheet.

Additional changes:
- Implement ASPEED PCIe root complex (TYPE_ASPEED_PCIE_RC).
- Wire up interrupt propagation via aspeed_pcie_rc_set_irq().
- Add tracepoints for config read/write and INTx handling.

Signed-off-by: Jamin Lin <jamin_lin@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250919093017.338309-4-jamin_lin@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

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