[Blackfin] arch: Allow concurrent use of GPIO and GPIO IRQ

The irq setup code no longer calls gpio request and free.
This patch also changes the default gpio_free behavior on Blackfin.
A freed GPIO keeps it's last state, and is not defaulted back to
an input. This is also what all other architectures do.

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