Blackfin: do not configure the UART early if on wrong processor

Before we configure the early UART, check to make sure we are running on
the expected processor - otherwise, we cause problems by configuring pins
that don't exist (and causing an infinite loop of faults).

Signed-off-by: Robin Getz <robin.getz@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>