bios: Add support for SGA

This patch creates new <bios> element which, at this time has only the
attribute useserial='yes|no'. This attribute allow users to use
Serial Graphics Adapter and see BIOS messages from the very first moment
domain boots up. Therefore, users can choose boot medium, set PXE, etc.

tests/qemuxml2argvdata/qemuxml2argv-bios.args

@@ -0,0 +1,6 @@
+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
+/usr/bin/qemu -S -M pc -m 1024 -smp 1 -nodefaults -device sga \
+-monitor unix:/tmp/test-monitor,server,nowait -no-acpi -boot c \
+-hda /dev/HostVG/QEMUGuest1 -serial pty \
+-usb -device usb-tablet,id=input0 -vnc 127.0.0.1:0 \
+-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3

tests/qemuxml2argvdata/qemuxml2argv-bios.xml

@@ -0,0 +1,39 @@
+<domain type='qemu'>
+  <name>test-bios</name>
+  <uuid>362d1fc1-df7d-193e-5c18-49a71bd1da66</uuid>
+  <memory>1048576</memory>
+  <currentMemory>1048576</currentMemory>
+  <vcpu>1</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+    <bootmenu enable='yes'/>
+    <bios useserial='yes'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>restart</on_crash>
+  <devices>
+   <emulator>/usr/bin/qemu</emulator>
+   <disk type='block' device='disk'>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+      <address type='drive' controller='0' bus='0' unit='0'/>
+    </disk>
+    <controller type='ide' index='0'/>
+    <serial type='pty'>
+      <target port='0'/>
+    </serial>
+    <console type='pty'>
+      <target type='serial' port='0'/>
+    </console>
+    <input type='tablet' bus='usb'/>
+    <input type='mouse' bus='ps2'/>
+    <graphics type='vnc' port='5900' autoport='no' listen='127.0.0.1'/>
+    <video>
+      <model type='cirrus' vram='9216' heads='1'/>
+    </video>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>