Convert CONFIG_SPL_SPI_SUPPORT to Kconfig

Move this option to Kconfig and tidy up existing uses.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/cgtqmx6eval_defconfig b/configs/cgtqmx6eval_defconfig
index 63e3942..83d3211 100644
--- a/configs/cgtqmx6eval_defconfig
+++ b/configs/cgtqmx6eval_defconfig
@@ -10,6 +10,7 @@
 CONFIG_SPL_MMC_SUPPORT=y
 CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL_SPI_FLASH_SUPPORT=y
+CONFIG_SPL_SPI_SUPPORT=y
 CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=arch/arm/imx-common/spl_sd.cfg,SPL,MX6QDL"
 CONFIG_BOOTDELAY=3
 CONFIG_SPL=y