ympd: needs <dlfcn.h>

Add a dependency on !BR2_STATIC_LIBS, since <dlfcn.h> is used. While
we're at it, we also fix the comment which was lacking the BR2_USE_MMU
dependency.

Fixes:

  http://autobuild.buildroot.org/results/30853c1011544f8b6a5d3b3852af93bef4c0f5cb/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>