ArmVirtPkg: unify HttpLib resolutions in "ArmVirt.dsc.inc"

ArmVirtPkg: unify HttpLib resolutions in "ArmVirt.dsc.inc"

We already resolve a number of networking-related library classes in
ArmVirt.dsc.inc; follow suit with HttpLib.

Cc: Julien Grall <julien.grall@linaro.org>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1007
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>