OvmfPkg: XenHypercallLib: add empty constructor for ARM & AARCH64

OvmfPkg: XenHypercallLib: add empty constructor for ARM & AARCH64

In the next patch we'll add a simple query function to the XenHypercallLib
library class that is supposed to be called by initialization code in
modules. Among those, in constructors of dependent libraries too.

Library construction ordering is ensured only between libraries with
constructors, plus we shouldn't allow a dependent library with a
constructor to call into any XenHypercallLib instances (the simple query
function) before XenHypercallLib is constructed itself. For this reason,
introduce an (empty) constructor for ARM & AARCH64 too.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16999 6f19259b-4bc3-4df7-8a09-765794883524