ArmVirtPkg/ArmVirt.dsc.inc: define TcpIoLib resolution unconditionally

ArmVirtPkg/ArmVirt.dsc.inc: define TcpIoLib resolution unconditionally

Commit 9a67ba261fe9 ("ArmVirtPkg: Replace obsoleted network drivers
from platform DSC/FDF") failed to take into account that the now
unconditionally included IScsiDxe.inf from NetworkPkg requires a
resolution for TcpIoLib. Since specifying such a resolution is harmless
for platforms that have no networking enabled, let's just fix things
by dropping the conditionals around it.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>