media: rkisp1: csi: Rename CSI functions with a common rkisp1_csi prefix

The CSI-related functions are not named consistently. Fix it by using a
common rkisp1_csi prefix.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Dafna Hirschfeld <dafna@fastmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>