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/theadorable_defconfig b/configs/theadorable_defconfig
index 8757c60..af29d9f 100644
--- a/configs/theadorable_defconfig
+++ b/configs/theadorable_defconfig
@@ -3,9 +3,9 @@
 CONFIG_TARGET_THEADORABLE=y
 CONFIG_DEFAULT_DEVICE_TREE="armada-xp-theadorable"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
-CONFIG_SPL=y
 CONFIG_FIT=y
 CONFIG_BOOTDELAY=3
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set