arm-bsp: remove dunfell u-boot support

u-boot version 2020.01 is not needed with dunfell not supported.  Remove
files and adjust the necessary.  Also, move tc0 support to match the
other BSPs

Change-Id: Ibc0f93a9eb0ca600a84b1399d77b35e6ae08753b
Signed-off-by: Jon Mason <jon.mason@arm.com>