serial: sh-sci: Restrict non-COMPILE_TEST compilation

Hardware supported by the driver is only found on SUPERH or
ARCH_SHMOBILE platforms. Restrict non-COMPILE_TEST compilation to them.

Cc: linux-serial@vger.kernel.org
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>