i2c: rcar_i2c: Remove the driver

Remove the rcar_i2c driver, since it's no longer used by any
board and will be superseded by a DM and DT capable variant.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>