Blackfin: fix booting with older bootroms (no EVT1)

When dropping jump block support, the assumption was that all bootroms
supported entry point redirection via the EVT1 register.  Unfortunately,
this turned out to be incorrect for the oldest Blackfin parts (BF533-0.2
and older and BF561).  No one really noticed earlier because these parts
usually are booted by bypassing the bootrom entirely, and older BF533
parts are not supported at all (too many anomalies).

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