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/apl-mrb/sdc_launch_1uos_aaag.xml

@@ -2,7 +2,6 @@
     <uos id="1">
 	<uos_type desc="UOS type">ANDROID</uos_type>
 	<rtos_type desc="UOS Realtime capability">no</rtos_type>
-	<cpu_num desc="max cpu number for vm">2</cpu_num>
 	<mem_size desc="UOS memory size in MByte">2048</mem_size>
 	<gvt_args desc="GVT argument for the vm">64 448 8</gvt_args>
 	<vbootloader desc="virtual bootloader method" readonly="true">ovmf</vbootloader>

misc/acrn-config/xmls/config-xmls/apl-mrb/sdc_launch_1uos_aliaag.xml

@@ -2,7 +2,6 @@
     <uos id="1">
 	<uos_type desc="UOS type">ALIOS</uos_type>
 	<rtos_type desc="UOS Realtime capability">no</rtos_type>
-	<cpu_num desc="max cpu number for vm">2</cpu_num>
 	<mem_size desc="UOS memory size in MByte">2048</mem_size>
 	<gvt_args desc="GVT argument for the vm">64 448 8</gvt_args>
 	<vbootloader desc="virtual bootloader method" readonly="true">ovmf</vbootloader>

misc/acrn-config/xmls/config-xmls/apl-mrb/sdc_launch_1uos_laag.xml

@@ -2,7 +2,6 @@
     <uos id="1">
 	<uos_type desc="UOS type">CLEARLINUX</uos_type>
 	<rtos_type desc="UOS Realtime capability">no</rtos_type>
-	<cpu_num desc="max cpu number for the vm">3</cpu_num>
 	<mem_size desc="UOS memory size in MByte">2048</mem_size>
 	<gvt_args desc="GVT argument for the vm">64 448 8</gvt_args>
 	<vbootloader desc="virtual bootloader method" readonly="true">ovmf</vbootloader>