media: rkisp1: Add helper function to swap colour channels

media: rkisp1: Add helper function to swap colour channels

The BLS parameters passed by userspace are specified for named colour
channels (R, Gr, Gb and B), while the hardware registers reference
positions in the 2x2 CFA pattern (A, B, C and D).

The BLS values are swapped based on the CFA pattern when writing to or
reading from registers, using hand-roled switch statements. The logic is
duplicated already, and new code will require similar processing. Move
the swap logic to a shared function, using static data to control the
channels order.

Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>