gpu: ipu-v3: Move i.MX IPUv3 core driver out of staging

The i.MX Image Processing Unit (IPU) contains a number of image processing
blocks that sit right in the middle between DRM and V4L2. Some of the modules,
such as Display Controller, Processor, and Interface (DC, DP, DI) or CMOS
Sensor Interface (CSI) and their FIFOs could be assigned to either framework,
but others, such as the dma controller (IDMAC) and image converter (IC) can
be used by both.
The IPUv3 core driver provides an internal API to access the modules, to be
used by both DRM and V4L2 IPUv3 drivers.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>