media: stm32: dcmi: addition of DMA-MDMA chaining support

media: stm32: dcmi: addition of DMA-MDMA chaining support

Add possibility to rely on an additional MDMA channel and chain
the DMA and MDMA channels allowing to achieve faster capture.
Indeed, on the MP15 platform, the MDMA engine has an higher
bandwidth to the DDR than the DMA engine.  Relying on that
it is possible to capture frames from the DCMI IP into the DDR
by using two channels as follow:

  DCMI -> (DMA) -> SRAM -> (MDMA) -> DDR

The DMA is able by himself to trigger a MDMA request hence, once
properly configured, the DCMI IP can simply trigger the DMA in order
to have the data pushed up to the DDR (via the SRAM and a MDMA
channel).

This behavior is detailed in the document
Documentation/arch/arm/stm32/stm32-dma-mdma-chaining.rst

Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>