DMA: shdma: switch all __iomem pointers to void

In the shdma driver __iomem pointers are used to point to hardware
registers.  Using typed pointers like "u32 __iomem *" in this case is
inconvenient, because then offsets, added to such pointers, have to be
devided by sizeof(u32) or similar. Switch the driver to use void
pointers, which avoids this clumsiness.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>