clk: renesas: rcar-gen3: Update description for RZ/G2

The rcar-gen3-cpg driver is also used on Renesas RZ/G2 SoC's, update the
description for the CLK_RCAR_GEN3_CPG config symbol to reflect this.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Chris Paterson <Chris.Paterson2@renesas.com>
Link: https://lore.kernel.org/r/20200911101703.20521-1-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>