rcar-du: add/rename DEFR6 TCON bits

The  TCNE2 bit  of the DEFR6 register was renamed to TCNE1 in the R-Car gen2
manuals -- which makes more  sense as that bit controls whether DU1, not DU2
is connected to TCON.

While at it, add the TCNE0 bit which controls whether DU0 is connected to
TCON.

Based on the large patch by Andrey Gusakov <andrey.gusakov@cogentembedded.com>.

Signed-off-by: Andrey Gusakov <andrey.gusakov@cogentembedded.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>