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/cairo_defconfig b/configs/cairo_defconfig
index 7d8fe11..f2daa38 100644
--- a/configs/cairo_defconfig
+++ b/configs/cairo_defconfig
@@ -1,9 +1,9 @@
 CONFIG_ARM=y
 CONFIG_OMAP34XX=y
 CONFIG_TARGET_OMAP3_CAIRO=y
-CONFIG_SPL=y
 CONFIG_BOOTDELAY=-2
 CONFIG_VERSION_VARIABLE=y
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="Cairo # "
 CONFIG_CMD_BOOTZ=y