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/pico-imx7d_defconfig b/configs/pico-imx7d_defconfig
index a6ee5ce..d79d3ea 100644
--- a/configs/pico-imx7d_defconfig
+++ b/configs/pico-imx7d_defconfig
@@ -26,6 +26,7 @@
 CONFIG_BOOTCOMMAND="run findfdt; run finduuid; run distro_bootcmd"
 CONFIG_DEFAULT_FDT_FILE="ask"
 CONFIG_SPL_MAX_SIZE=0xe000
+CONFIG_SPL_HAS_BSS_LINKER_SECTION=y
 CONFIG_SPL_BSS_MAX_SIZE=0x100000
 CONFIG_SPL_I2C=y
 CONFIG_SPL_USB_HOST=y