imx25-pdk: create ds1338 for qtest inside the test

There is no need to have a test device created by the board.
Instead, create it in the qtest so that we will be able to run
it on other boards too.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>