dmaengine: dw-edma: Mark emulated IRQ as level-triggered

The interrupt-emulation virtual IRQ uses handle_level_irq(), but the IRQ
descriptor has not been marked with IRQ_LEVEL.

The interrupt emulation is somewhat unusual: the eDMA interrupt handlers
dispatch the virtual IRQ for every edma_int[] interrupt because software
cannot reliably tell an interrupt-emulation event from one caused solely
by DONE/ABORT status. If an interrupt arrives before the doorbell
handler is registered for the virtual IRQ, the IRQ core marks it
pending. When the IRQ is later started, check_irq_resend() treats it as
non-level and replays the pending interrupt, causing the newly
registered handler to run for a stale event.

Mark the virtual IRQ with IRQ_LEVEL so the stale pending state is
cleared without being replayed. This was observed in pci_endpoint_test
as two doorbell handler calls when the DMA-variant test ran before
DOORBELL_TEST.

Fixes: d9d5e1bdd180 ("dmaengine: dw-edma: Add virtual IRQ for interrupt-emulation doorbells")
Cc: stable@vger.kernel.org
Reported-by: Niklas Cassel <cassel@kernel.org>
Closes: https://lore.kernel.org/r/ampndLtU32ODmncX@ryzen
Tested-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Koichiro Den <den@valinux.co.jp>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20260730160701.3550710-1-den@valinux.co.jp
Signed-off-by: Vinod Koul <vkoul@kernel.org>