Blackfin: bf537-stamp: drop ATA interrupt probe workaround

The interrupt probe workaround doesn't work without hacks to common code,
and the add-on card only needs a simple resistor to fix the problem, so
drop the board-specific hack.

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