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/Sinovoip_BPI_M2_defconfig b/configs/Sinovoip_BPI_M2_defconfig
index 181e1e2..267aaf8 100644
--- a/configs/Sinovoip_BPI_M2_defconfig
+++ b/configs/Sinovoip_BPI_M2_defconfig
@@ -6,8 +6,8 @@
 CONFIG_USB2_VBUS_PIN=""
 CONFIG_DEFAULT_DEVICE_TREE="sun6i-a31s-sinovoip-bpi-m2"
 # CONFIG_SYS_MALLOC_CLEAR_ON_INIT is not set
-CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="SUNXI_GMAC,RGMII"
+CONFIG_SPL=y
 # CONFIG_CMD_IMLS is not set
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_FPGA is not set