Blackfin: set bf51x/bf52x to 0.0 rev by default and bf54x to 0.2

Update the default revs based on what we actually support (bf54x-0.[01]
is too broken to use).

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>