clk: renesas: r8a77970: Add TPU clock

The TPU0 clock wasn't present in the original R8A77970 patch by Daisuke
Matsushita, it was added in a later BSP version...

Based on the original (and large) patch by Vladimir Barinov.

Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>