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/a3m071_defconfig b/configs/a3m071_defconfig
index c620183..e939121 100644
--- a/configs/a3m071_defconfig
+++ b/configs/a3m071_defconfig
@@ -1,10 +1,10 @@
 CONFIG_PPC=y
 CONFIG_MPC5xxx=y
 CONFIG_TARGET_A3M071=y
-CONFIG_SPL=y
 CONFIG_FIT=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_BOOTDELAY=3
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_LOOPW=y
 # CONFIG_CMD_SETEXPR is not set