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/difrnce_dit4350_defconfig b/configs/difrnce_dit4350_defconfig
index c76af0e..e42c358 100644
--- a/configs/difrnce_dit4350_defconfig
+++ b/configs/difrnce_dit4350_defconfig
@@ -14,8 +14,8 @@
 CONFIG_VIDEO_LCD_BL_PWM="PB2"
 CONFIG_DEFAULT_DEVICE_TREE="sun5i-a13-difrnce-dit4350"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
-CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="CONS_INDEX=2"
+CONFIG_SPL=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_FPGA is not set