gpio: port to am335x

* 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

distrib/sets/lists/minix/md.evbarm

@@ -13,6 +13,7 @@
 ./multiboot/mod10_vm			minix-sys
 ./multiboot/mod11_pfs			minix-sys
 ./multiboot/mod12_init			minix-sys
+./sbin/gpio				minix-sys
 ./usr/bin/eepromread			minix-sys
 ./usr/include/arm			minix-sys
 ./usr/include/arm/aeabi.h		minix-sys
@@ -108,7 +109,6 @@
 ./usr/sbin/bmp085			minix-sys
 ./usr/sbin/cat24c256			minix-sys
 ./usr/sbin/fb				minix-sys
-./usr/sbin/gpio				minix-sys
 ./usr/sbin/i2c				minix-sys
 ./usr/sbin/lan8710a			minix-sys
 ./usr/sbin/random			minix-sys