virtio GL: always announce gl support to guest

virtio GL: always announce gl support to guest

x86 emulator always needs to know if virtio GL support is enabled in QEMU. Currently
we only announce gl support to guest if QEMU is configurd with --enable-gl. When
configured with --disable-gl, QEMU doesn't announce GL support to guest while guest
assumes such a support by default. This results in incorrect operation of x86 emulator.
Fix this by always announcing virtio GL support to guest, it doesn't make any difference
for ARM emulator.

Signed-off-by: Igor Mitsyanko <i.mitsyanko@samsung.com>