dev/arm: get rid of AmbaDev namespace

dev/arm: get rid of AmbaDev namespace

It was confusing having an AmbaDev namespace along with an
AmbaDevice class.  The namespace stuff is now moved in to
a new base AmbaDevice class, which is a mixin for classes
AmbaPioDevice (the former AmbaDevice) and AmbaDmaDevice
to provide the readId function as an inherited member function.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>