amlogic: console: Move console driver to common directory

The code managing the console is the same for all the platforms
currently supported. Since it is unlikely to change in the future move
the code to an external file in the common directory.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>
Change-Id: I6df555ea82d483b4f08a4a1e2cb0a7488fbaa015