media: rzg2l-cru: Move register definitions to a separate file

Move the RZ/G2L CRU register definitions from `rzg2l-video.c` to a
dedicated header file, `rzg2l-cru-regs.h`. Separating these definitions
into their own file improves the readability of the code.

Suggested-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Link: https://lore.kernel.org/r/20241018133446.223516-23-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>