unicore32-softmmu: Add a minimal curses screen support

unicore32-softmmu: Add a minimal curses screen support

This patch adds a minimal curses screen support for unicore32-softmmu.
We assume 80*30 screen size to minimize the implementation.
Two problems are not solved, but they are innocuous.
1. curses windows will be blank when switching to monitor screen and back
2. backspace is not handled yet

v1->v2: add extra handler for '\r'

Signed-off-by: Zhang Mengchi <zhangmengchi@mprc.pku.edu.cn>
Signed-off-by: Guan Xuetao <gxt@mprc.pku.edu.cn>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>