python: added pyA20 for controlling GPIO

pyA20 allows controlling GPIO, SPI and I2C on Allwinner boards from python.
Although it is named A20 it should work on A10, A13 and other CPUs.
Provided by Olimex for their boards but should work for others as well.
Tested on A20-OLinuXino-MICRO.

Signed-off-by: Jens Lucius <info@jenslucius.com>
python: pyA20 added different GPIO mappings

Unfortunately there is a difference between different boards when using pyA20
- the GPIO mappings.
Olimex tried to solve this by providing different packages for different boards.
Just made the receipe use different mappings.h, so it can be easily adjusted
to different boards in one receipe.

Signed-off-by: Jens Lucius <info@jenslucius.com>
python: pyA20 depend on python and only for olimex boards

Add dependency on python and COMPATIBLE_MACHINE as pyA20 is only
compatible to three olimex boards right now.

Signed-off-by: Jens Lucius <info@jenslucius.com>
Merge pull request #77 from Noxenious/master

python: added pyA20 for controlling GPIO