* port libgpio to am335x.
* increase NR_IRQ to 16 to avoid too many IRQs requested error.
* move gpio binary to /sbin (that's where mount looks for drivers).
* fix bug that re-enabled banks that were disabled due to bad revision.
* fix padconf masks for dm37xx in gpio driver (should be 16-bit).
* fix a few typos in README.txt and comments.
Change-Id: I32374415a97135174c5224f76374a870909fa90c
