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/brppt1_spi_defconfig b/configs/brppt1_spi_defconfig
index fc1f1e6..4df9f37 100644
--- a/configs/brppt1_spi_defconfig
+++ b/configs/brppt1_spi_defconfig
@@ -1,11 +1,11 @@
 CONFIG_ARM=y
 CONFIG_TARGET_BRPPT1=y
-CONFIG_SPL=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_SYS_EXTRA_OPTIONS="SERIAL1,CONS_INDEX=1,SPI_BOOT,EMMC_BOOT"
 CONFIG_SPI_BOOT=y
 CONFIG_BOOTDELAY=-2
 CONFIG_VERSION_VARIABLE=y
+CONFIG_SPL=y
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y
 # CONFIG_CMD_IMI is not set