dragonboard410c: Increase default environment size.

Due to changes in distro environment, ENV_SIZE limit was reached on Dragonboard.
This patch increases environment size to 8KiB.

Signed-off-by: Mateusz Kulikowski <mateusz.kulikowski@gmail.com>

include/configs/dragonboard410c.h

@@ -129,7 +129,7 @@ REFLASH(dragonboard/u-boot.img, 8)\
 	BOOTENV
 
 #define CONFIG_ENV_IS_NOWHERE
-#define CONFIG_ENV_SIZE			0x1000
+#define CONFIG_ENV_SIZE			0x2000
 #define CONFIG_ENV_VARS_UBOOT_CONFIG
 #define CONFIG_SYS_NO_FLASH