dt-bindings: media: rkisp1: Add i.MX8MP ISP to compatible

The i.MX8MP ISP is compatbile with the rkisp1 driver. Add it to the list
of compatible strings. While at it, expand on the description of the
clocks to make it clear which clock in the i.MX8MP ISP they map to,
based on the names from the datasheet.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Tested-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>