clk: renesas: r8a7796: Add 3DGE and ZG support

The 3DGE and ZG clocks are necessary to support the 3D graphics.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/291462bea7ffc13f8218c1901dc384b576bfc2d6.1689599217.git.geert+renesas@glider.be