dmaengine: Revert "drivers/dma: remove unused support for MEMSET operations"

This reverts commit 48a9db46.

Some platforms actually need support for the memset operations. Bring it back.

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