dfu: tftp: Kconfig: Enable DFU_TFTP support on the am335x_boneblack_defconfig

This commit enables support for DFU_TFTP on the am335x bone black device.

Signed-off-by: Lukasz Majewski <l.majewski@majess.pl>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/configs/am335x_boneblack_defconfig b/configs/am335x_boneblack_defconfig
index 60339c8..f1ff65f 100644
--- a/configs/am335x_boneblack_defconfig
+++ b/configs/am335x_boneblack_defconfig
@@ -8,3 +8,4 @@
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_SPI_FLASH=y
+CONFIG_DFU_TFTP=y