acrn-config: enable item check for launch config tool

1. enable item check for acrn-dm args which set from webUI input.
2. remove 'cpu_num' tag from launch config xml.

v1-v2:
    1). add method to check 'cpu_num'/'mem_size' in config xml.

v2-v3:
    1). as 'vcpu_num' configured in scenario, the parameter for acrn-dm is no
longer needed, remove 'cpu_num' tag and its handler from launch config.
    2). add 'poweroff_channel' tag for generic config.

Tracked-On: #3811
Signed-off-by: Wei Liu <weix.w.liu@intel.com>
Acked-by: Victor Sun <victor.sun@intel.com>

misc/acrn-config/xmls/config-xmls/generic/sdc_launch_1uos.xml

@@ -8,6 +8,8 @@
 	<rootfs_dev desc=""></rootfs_dev>
 	<rootfs_img desc=""></rootfs_img>
 	<console_type desc="UOS console type"></console_type>
+	<poweroff_channel desc="the method of power off uos">
+	</poweroff_channel>
 
 	<passthrough_devices>
 		<usb_xdci desc="vm usb_xdci device"></usb_xdci>