dma: mv_xor: Remove dead code

The driver currently defines the USE_TIMER macro, but the timer-feature
is never used in the code. The XOR and CRC32 results are never used.

The 'unmap_xxx' fields are no longer needed, they were made obsolete
in commit: 54f8d501 dmaengine: remove DMA unmap from drivers.

Let's remove all this dead code.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>