clk: renesas: r8a77970: Add CMT clocks

Add the R8A77970 CMT module clocks.

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: Chris Paterson <chris.paterson2@renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>