drm/rcar-du: dsi: Convert register bits to BIT() macro

drm/rcar-du: dsi: Convert register bits to BIT() macro

Convert register bits to BIT() macro where applicable. This is done
automatically using regex 's@(1 << \([0-9]\+\))@BIT(\1)', except for
bitfields which are manually updated to use GENMASK().

Reviewed-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Link: https://patch.msgid.link/20251028232959.109936-11-marek.vasut+renesas@mailbox.org
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>