Some peripherals might generate an error interrupt shortly after the
data interrupt due to the fact that the peripheral isn't serviced fast
enough.  In most cases this isn't a problem and is expected behavior.
This hasn't been a problem on most parts since you simply don't request
the error interrupt (or you leave it disabled while there is an expected
state) and do the peripheral status checking in the data interrupt.

The Blackfin SIC allows people to prioritize data and error interrupts,
and the Blackfin CEC allows interrupts of equal or higher priority to
nest.  The current default settings gives error interrupts a higher
priority than data interrupts.  So if an error occurs while processing
the data interrupt, it will be serviced immediately.

However, the error interrupt on the BF537 SIC cannot be enabled on a
per-peripheral basis.  Once the error interrupt is enabled for one
peripheral, it is automatically enabled for all peripherals.

Therefore lower the default multiplexed error interrupt priority so
most people need not worry themselves with this issue.
Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>