PCI: dwc: ep: Expose integrated eDMA resources via EPC aux-resource API

PCI: dwc: ep: Expose integrated eDMA resources via EPC aux-resource API

Implement the EPC aux-resource API for DesignWare endpoint controllers
with integrated eDMA.

Currently, only report an interrupt-emulation doorbell register
(PCI_EPC_AUX_DOORBELL_MMIO), including its Linux IRQ and the write data
needed to trigger the interrupt.

If the DMA controller MMIO window is already exposed via a
platform-owned fixed BAR subregion, also provide the BAR number and
offset so EPF drivers can reuse it without reprogramming the BAR.

Signed-off-by: Koichiro Den <den@valinux.co.jp>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260414141514.1341429-4-den@valinux.co.jp