media: imx: imx7_mipi_csis: Set dual pixel mode for RAW formats

Based on code samples provided by NXP, the RAW formats require usage of
the dual pixel mode. This has been confirmed by testing RAW8 and RAW10
capture on i.MX8MM from an OV5640 sensor connected over CSI-2, which
doesn't work properly in single pixel mode. Enable dual pixel mode, even
though the exact effect of this mode isn't well documented in the
reference manual.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>