drm: rcar-du: Write ESCR and OTAR as CRTC registers

drm: rcar-du: Write ESCR and OTAR as CRTC registers

The ESCR and OTAR registers exist in each DU channel, but at different
offsets for odd and even channels. This led to usage of the group
register access API to write them, with offsets macros named ESCR/OTAR
and ESCR2/OTAR2 for the first and second ESCR/OTAR register in the group
respectively.

The names are confusing as it suggests that the ESCR/OTAR registers for
DU0 and DU2 are taken into account, especially with writes performed to
the group register access API.

Rename the offsets to ESCR/OTAR02 and ESCR/OTAR13, and use the CRTC
register access API to clarify the code. The offsets values are updated
accordingly.

Cosmetic patch, no functional changes intended.

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
[Squashed ESCR and OTAR changes in a single commit]
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>