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/arch/arm/mach-socfpga/Kconfig b/arch/arm/mach-socfpga/Kconfig
index 5be9eaa..964824b 100644
--- a/arch/arm/mach-socfpga/Kconfig
+++ b/arch/arm/mach-socfpga/Kconfig
@@ -19,6 +19,9 @@
 	default y
 
 config SPL_SPI_FLASH_SUPPORT
+	default y if SPL_SPI_SUPPORT
+
+config SPL_SPI_SUPPORT
 	default y if DM_SPI
 
 config TARGET_SOCFPGA_ARRIA5