arm/dt: 8610: change the command mode device node name

The device node name dsi_v2_truly_wvga_video is also used
by the video mode panel.  To distinguish the differences
between video mode and command mode panels, it is changed
to dsi_v2_truly_wvga_cmd which indicates it is for command
mode panel.

Change-Id: I5a10bbe2cc06e73cfc211ff106d337632e5c415e
Signed-off-by: Xiaoming Zhou <zhoux@codeaurora.org>