spi/tegra: depend instead of select TEGRA_SYSTEM_DMA

It's unlikely that anyone ever wants to turn off SYSTEM_DMA, but just in
case, it makes more sense to have the driver depend on it than select it.
Signed-off-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

drivers/spi/Kconfig

@@ -333,8 +333,7 @@ config SPI_STMP3XXX
 
 config SPI_TEGRA
 	tristate "Nvidia Tegra SPI controller"
-	depends on ARCH_TEGRA
-	select TEGRA_SYSTEM_DMA
+	depends on ARCH_TEGRA && TEGRA_SYSTEM_DMA
 	help
 	  SPI driver for NVidia Tegra SoCs