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/maxbcm_defconfig b/configs/maxbcm_defconfig
index 457e569..35005fc 100644
--- a/configs/maxbcm_defconfig
+++ b/configs/maxbcm_defconfig
@@ -25,6 +25,8 @@
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_DISPLAY_BOARDINFO_LATE=y
 CONFIG_SPL_MAX_SIZE=0x1bfd0
+CONFIG_SPL_HAS_BSS_LINKER_SECTION=y
+CONFIG_SPL_BSS_START_ADDR=0x40020000
 CONFIG_SPL_BSS_MAX_SIZE=0x4000
 CONFIG_SPL_SYS_MALLOC_SIMPLE=y
 # CONFIG_SPL_SHARES_INIT_SP_ADDR is not set