ti_armv7_common.h: Add CONFIG_CMD_EXT4_WRITE

Given that with config_distro_defaults.h we always have ext4 read
support, add in write support.

Signed-off-by: Tom Rini <trini@konsulko.com>

include/configs/ti_armv7_common.h

@@ -283,5 +283,6 @@
 #endif
 
 #include <config_distro_defaults.h>
+#define CONFIG_CMD_EXT4_WRITE
 
 #endif	/* __CONFIG_TI_ARMV7_COMMON_H__ */