Convert CONFIG_SPL_GD_ADDR to Kconfig

This converts the following to Kconfig:
   CONFIG_SPL_GD_ADDR

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/T2080RDB_revD_NAND_defconfig b/configs/T2080RDB_revD_NAND_defconfig
index d2b8df2..feba8e5 100644
--- a/configs/T2080RDB_revD_NAND_defconfig
+++ b/configs/T2080RDB_revD_NAND_defconfig
@@ -39,6 +39,7 @@
 CONFIG_SPL_SYS_CCSR_DO_NOT_RELOCATE=y
 CONFIG_SPL_FLUSH_IMAGE=y
 CONFIG_SPL_SKIP_RELOCATE=y
+CONFIG_SPL_GD_ADDR=0xfffc8000
 CONFIG_SPL_RELOC_STACK=0xfffd8000
 CONFIG_SPL_RELOC_MALLOC=y
 CONFIG_SPL_RELOC_MALLOC_ADDR=0xfffcb000