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/am65x_evm_r5_defconfig b/configs/am65x_evm_r5_defconfig
index b6b0075..fbe3aba 100644
--- a/configs/am65x_evm_r5_defconfig
+++ b/configs/am65x_evm_r5_defconfig
@@ -34,6 +34,8 @@
 CONFIG_SPL_SIZE_LIMIT_SUBTRACT_GD=y
 CONFIG_SPL_SIZE_LIMIT_SUBTRACT_MALLOC=y
 CONFIG_SPL_MAX_SIZE=0x58000
+CONFIG_SPL_HAS_BSS_LINKER_SECTION=y
+CONFIG_SPL_BSS_START_ADDR=0x41c7effc
 CONFIG_SPL_BSS_MAX_SIZE=0xc00
 CONFIG_SPL_SYS_REPORT_STACK_F_USAGE=y
 CONFIG_SPL_STACK_R=y