clk: renesas: Rename CLK_R8A7796 to CLK_R8A77960

Rename CONFIG_CLK_R8A7796 for R-Car M3-W (R8A77960) to
CONFIG_CLK_R8A77960, to avoid confusion with R-Car M3-W+ (R8A77961),
which will use CONFIG_CLK_R8A77961.

Extend the dependency of CONFIG_CLK_R8A77960 from CONFIG_ARCH_R8A7796 to
CONFIG_ARCH_R8A77960, to relax dependencies for a future rename of the
SoC configuration symbol.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20191023122941.12342-4-geert+renesas@glider.be