There are multiple shared Kconfig options between R-Car Gen3 and Gen4.
Keep the common options in Kconfig.64 and move the R-Car Gen3 specific
options into separate Kconfig.rcar3 . The Kconfig.rcar3 contains SoC
and board list, which is limited to R-Car Gen3.
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>