IPUv3 fixes for v3.18

* tag 'ipu-fixes-3.18' of git://git.pengutronix.de/git/pza/linux:
  gpu: ipu-v3: Kconfig: Remove SOC_IMX6SL from IMX_IPUV3_CORE Kconfig
  gpu: ipu-v3: ipu-smfc: Do not leave DEBUG defined
  gpu: ipu-v3: Return proper error on ipu_add_client_devices error path
  gpu: ipu-v3: Select GENERIC_IRQ_CHIP to fix build error

Adds ipu_smfc_set_watermark() which programs a channel's SMFC FIFO
levels at which the watermark signal is set and cleared.

Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Convert the smfc object to be specific to a single smfc channel.
Add ipu_smfc_{get|put} to retrieve and release a single smfc channel
for exclusive use, and add use counter to ipu_smfc_{enable|disable}.

Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Move the SMFC module enable/disable helpers into the ipu-smfc submodule.

Signed-off-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

Let's only define DEBUG for debugging purpose and not by default to avoid
printing debugging message unnecessarily.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>

The Sensor Multi Fifo Controller (SMFC) is used as a buffer between
the two CSIs (writing simultaneously) and up to four IDMAC channels.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>