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/k2l_evm_defconfig b/configs/k2l_evm_defconfig
index f0b1697..9205c92 100644
--- a/configs/k2l_evm_defconfig
+++ b/configs/k2l_evm_defconfig
@@ -7,6 +7,7 @@
 CONFIG_SPL_POWER_SUPPORT=y
 CONFIG_SPL_SERIAL_SUPPORT=y
 CONFIG_SPL_SPI_FLASH_SUPPORT=y
+CONFIG_SPL_SPI_SUPPORT=y
 CONFIG_DEFAULT_DEVICE_TREE="k2l-evm"
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_VERSION_VARIABLE=y