Add support for the PocketBeagle

[randyrossi]

• Platform/operating system (i.e. Raspberry Pi with Raspbian operating system,
  Windows 32-bit, Windows 64-bit, Mac OSX 64-bit, etc.): BeagleBone Pocket

• Python version (run python -version or python3 -version): N/A

• Error message you are receiving, including any Python exception traces: N/A

• List the steps to reproduce the problem below (if possible attach code or commands
  to run): The beaglebone pocket uses pin conventions like P1_## or P2_## (as opposed to P8_## or P9_##) which are key names not recognized by the table that maps pin names to kernel gpio numbers in source/common.c (specifically lookup_gpio_by_key() function). On the pocket beagle, /usr/bin/config-pin does recognize these and provides the mapping info. But in order to program via python, this table needs to be updated for the pocket beagle. I patched my local adafruit-beaglebone-io-python with my own mappings for the pins I wanted to use and it resolved my issue. So I think its just a matter of adding the P1_## P2_## entries and the pocket would be supported.

[pdp7]

@randyrossi Thanks for opening this issue. Support for the PocketBeagle has not been added yet. I'm not able to give a good estimate right now as to when I will be able to implement it. However, I would be happy to review any pull requests.

[pdp7]

Initial support for PocketBeagle added by @RobertCNelson in #173

[RobertCNelson]

@randyrossi

first image build with this enablement..

https://rcn-ee.net/rootfs/bb.org/testing/2017-10-17/stretch-iot/bone-debian-9.2-iot-armhf-2017-10-17-4gb.img.xz

[pdp7]

@randyrossi have you been able to try the image that @RobertCNelson linked above?

[randyrossi]

Yes I did. Just tried a simple gpio pin out and seems to work. Thx!