arm64: add Renesas R8A77965 support

Add configuration option for the R-Car M3-N (R8A77965) SoC.

Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>