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/P1020RDB-PD_SDCARD_defconfig b/configs/P1020RDB-PD_SDCARD_defconfig
index ea91b9e9..43391a9 100644
--- a/configs/P1020RDB-PD_SDCARD_defconfig
+++ b/configs/P1020RDB-PD_SDCARD_defconfig
@@ -31,6 +31,7 @@
 CONFIG_SPL_MMC_BOOT=y
 CONFIG_SPL_SYS_CCSR_DO_NOT_RELOCATE=y
 CONFIG_SPL_FLUSH_IMAGE=y
+CONFIG_SPL_GD_ADDR=0xf8f9c000
 CONFIG_SPL_RELOC_STACK=0xf8f9d000
 CONFIG_SPL_RELOC_MALLOC=y
 CONFIG_SPL_RELOC_MALLOC_ADDR=0xf8fa5000