ARM: dts: Leave Exynos5250 SPI controller disabled by default

Rather than requiring each board to explicitly disable the SPI controllers
it is not using instead require boards to enable those that they are using.
This is less work overall since normally at most one of the controllers is
in use and avoids issues caused by inappropriate pinmuxing.

Signed-off-by: Mark Brown <broonie@linaro.org>
Acked-by: Tomasz Figa <t.figa@samsung.com>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>