staging: sm7xx: remove the buggy 2D acceleration support

When scrolling the screen on the console with the 2D acceleration
support, the whole system may hang. for example, when copying some files
from another machine to YeeLoong netbook with the sm7xx video driver via
scp and when the screen output is enabled, the system may hang.

Before the bug is fixed, remove the 2D acceleration!

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: Teddy Wang <teddy.wang@siliconmotion.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>