zynq: add UART nodes to device tree to initialize UART with OF

zynq: add UART nodes to device tree to initialize UART with OF

Commit c9416b92 added OF UART initialization support
but aliases nodes are missing in device tree.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Tested-by: Masahiro Yamada <yamada.m@jp.panasonic.com> [on ZC706 board]
Tested-by: Michal Simek <michal.simek@xilinx.com> [on ZC702 board]
Signed-off-by: Michal Simek <michal.simek@xilinx.com>