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/am335x_evm_defconfig b/configs/am335x_evm_defconfig
index 65a9002..f88c4a0 100644
--- a/configs/am335x_evm_defconfig
+++ b/configs/am335x_evm_defconfig
@@ -2,12 +2,12 @@
 CONFIG_TARGET_AM335X_EVM=y
 CONFIG_SPL_STACK_R_ADDR=0x82000000
 CONFIG_DEFAULT_DEVICE_TREE="am335x-evm"
-CONFIG_SPL=y
-CONFIG_SPL_STACK_R=y
 CONFIG_FIT=y
 CONFIG_SYS_EXTRA_OPTIONS="NAND"
 CONFIG_SPL_LOAD_FIT=y
 CONFIG_VERSION_VARIABLE=y
+CONFIG_SPL=y
+CONFIG_SPL_STACK_R=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMLS is not set