Blackfin: bf537: demux port H mask A and emac rx ints

The BF537 SIC combines the gpio port H mask A interrupts with the
emac rx interrupt, so we need to demux this in software.

It also combines the gpio port H mask B and the emac tx interrupts,
and the watchdog and port F mask B interrupts, but since we don't
support mask B yet, just add the defines for now.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>