tests: drivers: dma: chan_blen_transfer: Add low footprint test variant

The nucleo c031c6 was filtered due to small ram size. However, the
application did fit when builed and run with west. We add a low footprint
variant of the test to also test on platforms with smaller size but where
the application fits.

Signed-off-by: Benjamin Björnsson <benjamin.bjornsson@gmail.com>