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/Empire_electronix_d709_defconfig b/configs/Empire_electronix_d709_defconfig
index 5f01760..85cdf51 100644
--- a/configs/Empire_electronix_d709_defconfig
+++ b/configs/Empire_electronix_d709_defconfig
@@ -15,8 +15,8 @@
 CONFIG_VIDEO_LCD_BL_PWM="PB2"
 CONFIG_DEFAULT_DEVICE_TREE="sun5i-a13-empire-electronix-d709"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
-CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="CONS_INDEX=2"
+CONFIG_SPL=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_FPGA is not set