If one of QEMU_CAPS_DEVICE_QXL_VGA or QEMU_CAPS_DEVICE_QXL is set the
other one will always be set as well because both devices are tied
together in QEMU.

The change of args files is caused by the presence of capability
QEMU_CAPS_DEVICE_VIDEO_PRIMARY which means it's safe to use
"-device qxl-vga" instead of "-vga qxl", see commit (e3f2686b) and
by the fact that if QEMU_CAPS_VGA_QXL is set QEMU_CAPS_DEVICE_QXL_VGA
and QEMU_CAPS_DEVICE_QXL would be set too (since we support only qemu
with "-device" option).
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>