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/mk802_defconfig b/configs/mk802_defconfig
index d38bc7f..47bbf62 100644
--- a/configs/mk802_defconfig
+++ b/configs/mk802_defconfig
@@ -4,8 +4,8 @@
 CONFIG_USB2_VBUS_PIN="PH12"
 CONFIG_DEFAULT_DEVICE_TREE="sun4i-a10-mk802"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
-CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="USB_EHCI"
+CONFIG_SPL=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_FPGA is not set