dmaengine: mv_xor: remove support for dmacap,* DT properties

The only reason why we had dmacap,* properties is because back when
DMA_MEMSET was supported, only one out of the two channels per engine
could do a memset operation. But this is something that the driver
already knows anyway, and since then, the DMA_MEMSET support has been
removed.

The driver is already well aware of what each channel supports and the
one to one mapping between Linux specific implementation details (such
as dmacap,interrupt enabling DMA_INTERRUPT) and DT properties is a
good indication that these DT properties are wrong.

Therefore, this commit simply gets rid of these dmacap,* properties,
they are now ignored, and the driver is responsible for knowing the
capabilities of the hardware with regard to the dmaengine subsystem
expectations.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>