ARM: shmobile: r8a7740 dtsi: add remaining DIV6 clocks

This adds the remaining DIV6 clocks and all possible parents for the SUB
clock.

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>