Blackfin arch: Fix BUG -- BF533 + 0.5 silicon + MPU + UART PIO -> crash

Apply ANOMALY_05000283 & ANOMALY_05000315
Workaround also to the EXCEPTION path.

Cover evt_ivhw also with ANOMALY_05000315
The Workaround needs to be prior to accesses (either read or write) to
any system MMR.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>