[dif/entropy_src] add unit tests for `dif_entropy_src_configure()`
[dif/entropy_src] add unit tests for `dif_entropy_src_configure()`

This adds more unit tests for `dif_entropy_src_configure()` to test bad
arguments.

Signed-off-by: Timothy Trippel <77eacc84f9735d3cbb55a271710be269fc3a5818@google.com>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan