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/imx8mp_dhcom_pdk2_defconfig b/configs/imx8mp_dhcom_pdk2_defconfig
index cc815ac..5aca5fe 100644
--- a/configs/imx8mp_dhcom_pdk2_defconfig
+++ b/configs/imx8mp_dhcom_pdk2_defconfig
@@ -46,6 +46,8 @@
 CONFIG_ARCH_MISC_INIT=y
 CONFIG_BOARD_LATE_INIT=y
 CONFIG_SPL_MAX_SIZE=0x25000
+CONFIG_SPL_HAS_BSS_LINKER_SECTION=y
+CONFIG_SPL_BSS_START_ADDR=0x96fc00
 CONFIG_SPL_BSS_MAX_SIZE=0x400
 CONFIG_SPL_BOOTROM_SUPPORT=y
 # CONFIG_SPL_RAW_IMAGE_SUPPORT is not set