test/py: Allow any unit test suite to be found

test/py: Allow any unit test suite to be found

The u-boot.sym file is scanned to find unit test suites for execution. At
present it only finds those whose names start with 'dm' or 'env'. This
code is buried in the bowels of the test code so when adding a new suite
it is not easy to discover why it is ignored by the test framework.

There seems to be no need to make this restriction. Drop it.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Stephen Warren <swarren@nvidia.com>