env: Add CONFIG_SYS_RELOC_GD_ENV_ADDR symbol

Today in initr_reloc_global_data() we use some non-obvious tests to
determine if we need to relocate the env_addr within gd or not.  In
order to facilitate migration of other symbols to Kconfig we need to
introduce a new symbol for this particular use case.

Cc: Wolfgang Denk <wd@denx.de>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/P2020RDB-PC_SDCARD_defconfig b/configs/P2020RDB-PC_SDCARD_defconfig
index 7c43b95..7768fd1 100644
--- a/configs/P2020RDB-PC_SDCARD_defconfig
+++ b/configs/P2020RDB-PC_SDCARD_defconfig
@@ -44,6 +44,7 @@
 CONFIG_OF_CONTROL=y
 CONFIG_DEFAULT_DEVICE_TREE="p2020rdb-pc"
 CONFIG_ENV_IS_IN_MMC=y
+CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_DM=y
 CONFIG_FSL_ESDHC=y
 CONFIG_MTD_NOR_FLASH=y