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/ma5d4evk_defconfig b/configs/ma5d4evk_defconfig
index e3431ae..b273da1 100644
--- a/configs/ma5d4evk_defconfig
+++ b/configs/ma5d4evk_defconfig
@@ -1,11 +1,11 @@
 CONFIG_ARM=y
 CONFIG_ARCH_AT91=y
 CONFIG_TARGET_MA5D4EVK=y
-CONFIG_SPL=y
 CONFIG_FIT=y
 CONFIG_SYS_EXTRA_OPTIONS="SAMA5D4"
 CONFIG_BOOTDELAY=3
 CONFIG_VERSION_VARIABLE=y
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set