Blackfin arch: reset POLAR setting when acquiring a gpio for the first time

when requesting a GPIO for the first time, the POLAR setting is not
set to a sane state.  this can lead to indeterminate behavior that
cannot be resolved without an explicit write to the Blackfin port POLAR
register.

when requesting a GPIO for the first time via gpio_request(), the POLAR
setting for the GPIO in question should be set to sane state.  this
should occur if the GPIO has not been allocated in any other way.

some examples:
 - when doing something like "request_irq(); gpio_request();" on the
   same GPIO, the POLAR setting should not be reset.
 - when doing "gpio_request(); gpio_request();" on the same GPIO, the
   POLAR setting should be reset only the first time and not the second.

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