ARM: dts: r8a7740: Add CEU0

Describe CEU0 peripheral for Renesas R-Mobile A1 R8A7740 Soc.

Reported-by: Geert Uytterhoeven <geert@glider.be>
Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
[simon: dropped clock-names property]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>