This patch adds puv3 dma (Direct Memory Access) support,
include dma device simulation for kernel booting.
v1->v2: Add initialization to ret in puv3_dma_read.
Signed-off-by: Guan Xuetao <gxt@mprc.pku.edu.cn>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
