clk: renesas: cpg-mssr: Add support for R-Car M3-N

Initial support for R-Car M3-N (r8a77965), including core and module
clocks.

Based on Table 8.2d of "R-Car Series, 3rd Generation User's Manual:
Hardware (Rev. 0.80, Oct 31, 2017)".

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>