uart: barebones uart module added.

* Only defined call is the init. Will then expose the uart from
* the multiplexors.

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>
intel_galileo_rev_d: add uart definitions.

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>
uart_setup: add example on current uart use.

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>