Blackfin: BF537: push down error masks to avoid namespace pollution

The error masks are only needed in the BF537 demux error code, so instead
of needing all the short peripheral defines in global space, push these
masks into the one file where they are actually needed.  This fixes a
bunch of define collisions with common code (can/serial/etc...).

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Barry Song <barry.song@analog.com>