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/i12-tvbox_defconfig b/configs/i12-tvbox_defconfig
index 54fa819..e80f172 100644
--- a/configs/i12-tvbox_defconfig
+++ b/configs/i12-tvbox_defconfig
@@ -5,8 +5,8 @@
 CONFIG_VIDEO_COMPOSITE=y
 CONFIG_DEFAULT_DEVICE_TREE="sun7i-a20-i12-tvbox"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
-CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="SUNXI_GMAC,MACPWR=SUNXI_GPH(21)"
+CONFIG_SPL=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_FPGA is not set