ata: fix R-Car SATA driver dependencies

Make sata_rcar host driver depend on ARCH_SHMOBILE config option as
Renesas R-Car SATA support is specific to Renesas SoCs and the driver
to work requires suitable device tree node (or platform device) to be
defined.  Additionally allow the driver build if COMPILE_TEST config
option is set.

Cc: Simon Horman <horms@verge.net.au>
Cc: Magnus Damm <magnus.damm@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Tejun Heo <tj@kernel.org>