gdb: add support for Blackfin gdbserver

This requires removing "deprecated" markings from gdb-6.6, but this isn't
that big of a deal.  That is the last version with Blackfin support at the
moment and we're in the process of getting mainlined.

[Peter: only mark as undeprecated on bfin]
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>