ARM: renesas: Enable CONFIG_ENV_VARS_UBOOT_CONFIG on all boards

The CONFIG_ENV_VARS_UBOOT_CONFIG extends U-Boot environment with
variables arch/board/board_name/soc/vendor, which can be used to
discern different devices from each other based purely on U-Boot
environment variables.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>