Convert CONFIG_SPL_SPI_FLASH_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/taurus_defconfig b/configs/taurus_defconfig
index 74fc4d2..d11e93d 100644
--- a/configs/taurus_defconfig
+++ b/configs/taurus_defconfig
@@ -6,6 +6,7 @@
 CONFIG_SPL_LIBGENERIC_SUPPORT=y
 CONFIG_SPL_NAND_SUPPORT=y
 CONFIG_SPL_SERIAL_SUPPORT=y
+CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_DEFAULT_DEVICE_TREE="at91sam9g20-taurus"
 CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9G20,MACH_TYPE=2067,BOARD_TAURUS"
 CONFIG_BOOTDELAY=3