Kconfig: Move SPL settings into their own file

Move the SPL settings into common/spl where most of the SPL code is kept.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/polaroid_mid2407pxe03_defconfig b/configs/polaroid_mid2407pxe03_defconfig
index 9bf6fbf..2ac6f4c 100644
--- a/configs/polaroid_mid2407pxe03_defconfig
+++ b/configs/polaroid_mid2407pxe03_defconfig
@@ -15,8 +15,8 @@
 CONFIG_VIDEO_LCD_BL_PWM="PH0"
 CONFIG_DEFAULT_DEVICE_TREE="sun8i-a23-polaroid-mid2407pxe03"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
-CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="CONS_INDEX=5"
+CONFIG_SPL=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_FPGA is not set