Convert CONFIG_SPL_BSS_START_ADDR to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_BSS_START_ADDR

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/rut_defconfig b/configs/rut_defconfig
index 576be6c..8ef5386 100644
--- a/configs/rut_defconfig
+++ b/configs/rut_defconfig
@@ -36,6 +36,7 @@
 # CONFIG_DISPLAY_CPUINFO is not set
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_ARCH_MISC_INIT=y
+CONFIG_SPL_BSS_START_ADDR=0x80000000
 CONFIG_SPL_I2C=y
 CONFIG_SPL_NAND_DRIVERS=y
 CONFIG_SPL_NAND_ECC=y