dmaengine: sf-pdma: move macro to header file

The place where the macro, SF_PDMA_REG_BASE(), is cause kernel-doc
using wrong function declaration. Move it to header file.

Signed-off-by: Green Wan <green.wan@sifive.com>
Link: https://lore.kernel.org/r/20191118143554.16129-2-green.wan@sifive.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>