arm: mvebu: Espressobin: Set default value for $fdtfile env variable

On Espressobin board value for $fdtfile cannot be determined at compile
time and is calculated at board runtime code. This change uses a new option
DEFAULT_ENV_IS_RW to allow modifying default_environment[] array at runtime
and set into it correct value.

This change also ensure that 'env default -a' set correct value to $fdtfile.

Signed-off-by: Pali Rohár <pali@kernel.org>
Acked-by: Andre Heider <a.heider@gmail.com>
diff --git a/include/configs/mvebu_armada-37xx.h b/include/configs/mvebu_armada-37xx.h
index 0d58560..6df7023 100644
--- a/include/configs/mvebu_armada-37xx.h
+++ b/include/configs/mvebu_armada-37xx.h
@@ -58,6 +58,11 @@
 #define CONFIG_MTD_PARTITIONS		/* required for UBI partition support */
 
 /*
+ * Environment
+ */
+#define DEFAULT_ENV_IS_RW		/* required for configuring default fdtfile= */
+
+/*
  * Ethernet Driver configuration
  */
 #define CONFIG_ARP_TIMEOUT	200
@@ -87,6 +92,11 @@
 
 #include <config_distro_bootcmd.h>
 
+/* filler for default values filled by board_early_init_f() */
+#define ENV_RW_FILLER \
+	"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0" /* for fdtfile= */ \
+	""
+
 /* fdt_addr and kernel_addr are needed for existing distribution boot scripts */
 #define CONFIG_EXTRA_ENV_SETTINGS	\
 	"scriptaddr=0x6d00000\0"	\
@@ -96,6 +106,7 @@
 	"kernel_addr=0x7000000\0"	\
 	"kernel_addr_r=0x7000000\0"	\
 	"ramdisk_addr_r=0xa000000\0"	\
-	BOOTENV
+	BOOTENV \
+	ENV_RW_FILLER
 
 #endif /* _CONFIG_MVEBU_ARMADA_37XX_H */