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/ls2080ardb_nand_defconfig b/configs/ls2080ardb_nand_defconfig
index 7304c4d..17fe433 100644
--- a/configs/ls2080ardb_nand_defconfig
+++ b/configs/ls2080ardb_nand_defconfig
@@ -41,6 +41,8 @@
 CONFIG_RESET_PHY_R=y
 CONFIG_SPL_MAX_SIZE=0x16000
 CONFIG_SPL_PAD_TO=0x80000
+CONFIG_SPL_HAS_BSS_LINKER_SECTION=y
+CONFIG_SPL_BSS_START_ADDR=0x80100000
 CONFIG_SPL_BSS_MAX_SIZE=0x100000
 # CONFIG_SPL_SHARES_INIT_SP_ADDR is not set
 CONFIG_SPL_STACK=0x18009ff0