Convert CONFIG_ENABLE_36BIT_PHYS to Kconfig

This converts the following to Kconfig:
   CONFIG_ENABLE_36BIT_PHYS

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/P2020RDB-PC_NAND_defconfig b/configs/P2020RDB-PC_NAND_defconfig
index 5a62055..9a42388 100644
--- a/configs/P2020RDB-PC_NAND_defconfig
+++ b/configs/P2020RDB-PC_NAND_defconfig
@@ -14,6 +14,7 @@
 CONFIG_MPC85xx=y
 # CONFIG_CMD_ERRATA is not set
 CONFIG_TARGET_P2020RDB=y
+CONFIG_ENABLE_36BIT_PHYS=y
 CONFIG_SYS_MPC85XX_NO_RESETVEC=y
 CONFIG_TPL_SYS_MPC85XX_NO_RESETVEC=y
 CONFIG_MP=y