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/twister_defconfig b/configs/twister_defconfig
index 42b88fb..ad6cd96 100644
--- a/configs/twister_defconfig
+++ b/configs/twister_defconfig
@@ -1,9 +1,9 @@
 CONFIG_ARM=y
 CONFIG_OMAP34XX=y
 CONFIG_TARGET_TWISTER=y
-CONFIG_SPL=y
 CONFIG_FIT=y
 CONFIG_BOOTDELAY=10
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="twister => "
 # CONFIG_CMD_IMLS is not set