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/imx8qm_rom7720_a1_4G_defconfig b/configs/imx8qm_rom7720_a1_4G_defconfig
index 62c1f03..5e32568 100644
--- a/configs/imx8qm_rom7720_a1_4G_defconfig
+++ b/configs/imx8qm_rom7720_a1_4G_defconfig
@@ -28,6 +28,8 @@
 CONFIG_LOG=y
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_SPL_MAX_SIZE=0x1f000
+CONFIG_SPL_HAS_BSS_LINKER_SECTION=y
+CONFIG_SPL_BSS_START_ADDR=0x128000
 CONFIG_SPL_BSS_MAX_SIZE=0x1000
 CONFIG_SPL_BOARD_INIT=y
 CONFIG_SPL_POWER_DOMAIN=y