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_qspi_defconfig b/configs/ls1021atwr_sdcard_qspi_defconfig
index 70eb312..a7c1a04 100644
--- a/configs/ls1021atwr_sdcard_qspi_defconfig
+++ b/configs/ls1021atwr_sdcard_qspi_defconfig
@@ -1,7 +1,6 @@
 CONFIG_ARM=y
 CONFIG_TARGET_LS1021ATWR=y
 CONFIG_DEFAULT_DEVICE_TREE="ls1021a-twr-duart"
-CONFIG_SPL=y
 CONFIG_FIT=y
 CONFIG_FIT_VERBOSE=y
 CONFIG_OF_BOARD_SETUP=y
@@ -9,6 +8,7 @@
 CONFIG_SYS_EXTRA_OPTIONS="RAMBOOT_PBL,SPL_FSL_PBL,SD_BOOT,SD_BOOT_QSPI"
 CONFIG_SD_BOOT=y
 CONFIG_BOOTDELAY=3
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set