i2c: shmobile/rcar: Restrict non-COMPILE_TEST compilation

Hardware supported by the i2c sh_mobile and rcar drivers is only found
on SUPERH or ARCH_SHMOBILE platforms. Restrict non-COMPILE_TEST
compilation to them.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>