Move console drivers to AArch64 folder ...

This patch moves the various assembly console drivers
into `aarch64` architecture specific folder. Stub files,
which include files from new location, are retained at the
original location for platform compatibility reasons.

Change-Id: I0069b6c1c0489ca47f5204d4e26e3bc3def533a8

drivers: Add Cadence UART driver ...

Add a driver for the Cadence UART which is found in Xilinx Zynq SOCs.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>