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/Marsboard_A10_defconfig b/configs/Marsboard_A10_defconfig
index cef9794..b1d6b23 100644
--- a/configs/Marsboard_A10_defconfig
+++ b/configs/Marsboard_A10_defconfig
@@ -3,8 +3,8 @@
 CONFIG_MACH_SUN4I=y
 CONFIG_DEFAULT_DEVICE_TREE="sun4i-a10-marsboard"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
-CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="SUNXI_EMAC,AHCI"
+CONFIG_SPL=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_FPGA is not set