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/sama5d3xek_spiflash_defconfig b/configs/sama5d3xek_spiflash_defconfig
index ab681fd..2754920 100644
--- a/configs/sama5d3xek_spiflash_defconfig
+++ b/configs/sama5d3xek_spiflash_defconfig
@@ -37,6 +37,8 @@
 CONFIG_BOOTCOMMAND="sf probe 0; sf read 0x21000000 0x60000 0xc000; sf read 0x22000000 0x6c000 0x394000; bootz 0x22000000 - 0x21000000"
 # CONFIG_DISPLAY_BOARDINFO is not set
 CONFIG_SPL_MAX_SIZE=0x18000
+CONFIG_SPL_HAS_BSS_LINKER_SECTION=y
+CONFIG_SPL_BSS_START_ADDR=0x20000000
 CONFIG_SPL_BSS_MAX_SIZE=0x80000
 # CONFIG_SPL_SHARES_INIT_SP_ADDR is not set
 CONFIG_SPL_STACK=0x318000