board: atmel: sama7g5ek: avoid rewriting of configured CONFIG_BOOTCOMMAND

Rewrite the CONFIG_BOOTCOMMAND only if it's not previously configured from
defconfig file.
This allows the user to select from defconfig/menuconfig the desired
boot command.
Adjust the current board defconfigs to reflect the default booting command
for the specific ENV configuration.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
diff --git a/include/configs/sama7g5ek.h b/include/configs/sama7g5ek.h
index ddf4f0b..9b7cc2c 100644
--- a/include/configs/sama7g5ek.h
+++ b/include/configs/sama7g5ek.h
@@ -24,7 +24,7 @@
 	 GENERATED_GBL_DATA_SIZE)
 #endif
 
-#undef CONFIG_BOOTCOMMAND
+#ifndef CONFIG_BOOTCOMMAND
 #ifdef CONFIG_SD_BOOT
 /* u-boot env in sd/mmc card */
 
@@ -32,6 +32,10 @@
 #define CONFIG_BOOTCOMMAND	"fatload mmc " CONFIG_ENV_FAT_DEVICE_AND_PART " 0x61000000 at91-sama7g5ek.dtb; " \
 				"fatload mmc " CONFIG_ENV_FAT_DEVICE_AND_PART " 0x62000000 zImage; " \
 				"bootz 0x62000000 - 0x61000000"
+#else
+#define CONFIG_BOOTCOMMAND	"Place your bootcommand here"
+#endif
+
 #endif
 
 #define CONFIG_ARP_TIMEOUT		200