ARM: renesas: Disable EFI on R-Car Gen2

These systems are unlikely to use EFI as this functionality has not been
enabled until it got pulled in by Kconfig default. This functionality
does add some 60-70 kiB to the u-boot.img size, which overflows the size
limit. Disable it.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Paul Barker <paul.barker.ct@bp.renesas.com>