clk: shmobile: Add r8a7793 support

R-Car M2N (r8a7793) clock is handled in R-Car Gen2 clock driver.

Signed-off-by: Hisashi Nakamura <hisashi.nakamura.ak@renesas.com>
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>