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/sama5d4_xplained_spiflash_defconfig b/configs/sama5d4_xplained_spiflash_defconfig
index ccc9298..461e29a 100644
--- a/configs/sama5d4_xplained_spiflash_defconfig
+++ b/configs/sama5d4_xplained_spiflash_defconfig
@@ -1,10 +1,10 @@
 CONFIG_ARM=y
 CONFIG_ARCH_AT91=y
 CONFIG_TARGET_SAMA5D4_XPLAINED=y
-CONFIG_SPL=y
 CONFIG_FIT=y
 CONFIG_SYS_EXTRA_OPTIONS="SAMA5D4,SYS_USE_SERIALFLASH"
 CONFIG_BOOTDELAY=3
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set