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/socfpga_sr1500_defconfig b/configs/socfpga_sr1500_defconfig
index 2a4494f..19731d1 100644
--- a/configs/socfpga_sr1500_defconfig
+++ b/configs/socfpga_sr1500_defconfig
@@ -3,11 +3,11 @@
 CONFIG_TARGET_SOCFPGA_SR1500=y
 CONFIG_SPL_STACK_R_ADDR=0x00800000
 CONFIG_DEFAULT_DEVICE_TREE="socfpga_cyclone5_sr1500"
+CONFIG_FIT=y
+CONFIG_VERSION_VARIABLE=y
 CONFIG_SPL=y
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 CONFIG_SPL_STACK_R=y
-CONFIG_FIT=y
-CONFIG_VERSION_VARIABLE=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set