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/ls1021atwr_sdcard_ifc_defconfig b/configs/ls1021atwr_sdcard_ifc_defconfig
index 439121d..ecc6b73 100644
--- a/configs/ls1021atwr_sdcard_ifc_defconfig
+++ b/configs/ls1021atwr_sdcard_ifc_defconfig
@@ -1,6 +1,5 @@
 CONFIG_ARM=y
 CONFIG_TARGET_LS1021ATWR=y
-CONFIG_SPL=y
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
@@ -8,6 +7,7 @@
 CONFIG_SYS_EXTRA_OPTIONS="RAMBOOT_PBL,SPL_FSL_PBL,SD_BOOT"
 CONFIG_SD_BOOT=y
 CONFIG_BOOTDELAY=3
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_GREPENV=y