Add a function to map the ring buffer with BusMasterCommonBuffer so that ring can be accessed by both guest and hypervisor. Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Jordan Justen <jordan.l.justen@intel.com> Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: Laszlo Ersek <lersek@redhat.com> Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Brijesh Singh <brijesh.singh@amd.com> [lersek@redhat.com: fix typo in commit message] Reviewed-by: Laszlo Ersek <lersek@redhat.com> Regression-tested-by: Laszlo Ersek <lersek@redhat.com>