timbgpio: add support for interrupt triggering on both flanks

Introduce support for triggering interrupts on both rising and falling
edge.

This feature requires version 3 or newer of the IP, a version check is
done when triggering on both edges is requested.

Signed-off-by: Richard Röjfors <richard.rojfors@pelagicore.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>