ARM: S3C64XX: SPI: Make platform device compilation selectable

The SPI controller platform devices should be compiled in
independent of the driver support, otherwise we might end
up with dev-spi built as kernel module.
Change this to make every machine select if it has some SPI
device and wants to build device definitions.

Signed-off-by: Jassi Brar <jassi.brar@samsung.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>