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/ti816x_evm_defconfig b/configs/ti816x_evm_defconfig
index 7df29cc..f8b14a0 100644
--- a/configs/ti816x_evm_defconfig
+++ b/configs/ti816x_evm_defconfig
@@ -1,8 +1,8 @@
 CONFIG_ARM=y
 CONFIG_TARGET_TI816X_EVM=y
-CONFIG_SPL=y
 CONFIG_BOOTDELAY=3
 CONFIG_VERSION_VARIABLE=y
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="u-boot/ti816x# "
 # CONFIG_CMD_IMLS is not set