clk: renesas: r8a7796: Add R8A77961 CPG/MSSR support

Add support for the R-Car M3-W+ (R8A77961) SoC.
R-Car M3-W+ is very similar to R-Car M3-W (R8A77960), which allows for
both SoCs to share a driver.

Based on Linux commit 2ba738d56db4 ("clk: renesas: r8a7796: Add R8A77961
CPG/MSSR support")

Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Signed-off-by: Hai Pham <hai.pham.ud@renesas.com>
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>