Blackfin: fix misnomer of some I-pipe helpers

__ipipe_{stall, unstall}_root_raw() identifiers may leave the reader
under the impression that only the virtual state is affected by these
operations, which is wrong. Pick names following the convention used
throughout the interrupt pipeline code.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>