Documentation: devicetree: Update samsung UART bindings

The primary purpose of this patch is to add information about (now
required) aliases of UART ports. However the documentation currently is
heavily outdated and so this patch also takes care of this.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>