Maintainers: specify the scope for OvmfPkg/ArmVirtPkg Xen module reviewers

Maintainers: specify the scope for OvmfPkg/ArmVirtPkg Xen module reviewers

We can use the format introduced under MdeModulePkg to clarify the
reviewership scopes a little. This should decrease the review spam that
Xen reviewers get.

Cc: Andrew Fish <afish@apple.com>
Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Julien Grall <julien.grall@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
[lersek@redhat.com: resolve conflict with commit 98fc52c44eee]