arm64: dts: renesas: Prepare for rename of ARCH_R8A7796 to ARCH_R8A77960

CONFIG_ARCH_R8A7796 for R-Car M3-W (R8A77960) will be renamed to
CONFIG_ARCH_R8A77960, to avoid confusion with R-Car M3-W+ (R8A77961),
which will use CONFIG_ARCH_R8A77961.

Relax dependencies by handling both symbols.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/20191023123342.13100-8-geert+renesas@glider.be