[Blackfin] arch:Fix BUG [#3876] pfbutton test for BTN3 on bf533 don't show complete info

 - Buttons on the BF533-STAMP board are not inverted
 - Fix spurious GPIO Interrupt caused during set irq_type for edge triggered interrupts

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>