dmaengine: dw-edma: Add interrupt-emulation hooks

dmaengine: dw-edma: Add interrupt-emulation hooks

DesignWare eDMA instances support "interrupt emulation", where a
software write can assert the IRQ line without setting the normal
DONE/ABORT status bits.

Introduce core callbacks needed to support this feature:

  - .ack_emulated_irq(): core-specific sequence to deassert an emulated
    IRQ
  - .db_offset(): offset from the DMA register base that is suitable as a
    host-writable doorbell target for interrupt emulation

Implement both hooks for the v0 register map. For dw-hdma-v0, provide a
stub .db_offset() returning ~0 until the correct offset is known.

The next patch wires these hooks into the dw-edma IRQ path and exports
the doorbell resources to platform users.

Signed-off-by: Koichiro Den <den@valinux.co.jp>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260215152216.3393561-2-den@valinux.co.jp
Signed-off-by: Vinod Koul <vkoul@kernel.org>