clk: renesas: cpg-mssr: add R8A77980 support

Add R-Car V3H (R8A77980) Clock Pulse Generator / Module Standby and
Software Reset support,  using the CPG/MSSR driver core and the common
R-Car Gen3 code.

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: Rob Herring <robh@kernel.org>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>