TARGET_DUMMY was introduced to resolve the same problem as commit 
"arch: Make board selection choices optional"
http://git.denx.de/?p=u-boot.git;a=commit;h=a26cd04920dc069fd6e91abb785426cf6c29f45f



Latter implementation is much cleaner and appropriate.

And anyways TARGET_DUMMY is no longer required.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>