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/chromebook_jerry_defconfig b/configs/chromebook_jerry_defconfig
index 5335aa5..9462433 100644
--- a/configs/chromebook_jerry_defconfig
+++ b/configs/chromebook_jerry_defconfig
@@ -7,6 +7,7 @@
 CONFIG_ROCKCHIP_RK3288=y
 CONFIG_TARGET_CHROMEBOOK_JERRY=y
 CONFIG_ROCKCHIP_FAST_SPL=y
+CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_SPL_STACK_R_ADDR=0x80000
 CONFIG_DM_KEYBOARD=y
 CONFIG_DEFAULT_DEVICE_TREE="rk3288-jerry"