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/smartweb_defconfig b/configs/smartweb_defconfig
index cf8bff6..6dc2fd5 100644
--- a/configs/smartweb_defconfig
+++ b/configs/smartweb_defconfig
@@ -2,10 +2,10 @@
 CONFIG_ARCH_AT91=y
 CONFIG_TARGET_SMARTWEB=y
 CONFIG_DEFAULT_DEVICE_TREE="at91sam9260-smartweb"
-CONFIG_SPL=y
 CONFIG_FIT=y
 CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9260"
 CONFIG_BOOTDELAY=3
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="U-Boot# "
 CONFIG_AUTOBOOT_KEYED=y