drivers: video: stm32_dcmipp: move video/ header directory to drivers/

During #89407 a driver-specific header stm32_dcmipp.h got introduced to
support new functionnalities not yet covered by video APIs.
Move this header into a new <include/zephyr/drivers/video/> include
direcctory like what other driver classes do.

Signed-off-by: Josuah Demangeon <me@josuah.net>