MLK-15001-10 gpu: Add dpu base driver

MLK-15001-10 gpu: Add dpu base driver

DPU is the display processing unit embedded in i.MX8qm and i.MX8qxp.
It was originally designed by Fujitsu.
The first revision has capture controller, display controller and blit engine.
The second revision is a lite one and has display controller and blit engine.
This patch adds a base driver for DPU, which provides a thin register wrapper,
interrurpt support and client platform device register for the upper layer to
use.  Currently, the driver only supports the display controller at the pixel
processing level and only the fetchdecodes are supported/tested as the fetch
units.

Signed-off-by: Liu Ying <victor.liu@nxp.com>