OvmfPkg/IoMmuDxe: Add SEV support for reserved shared memory
Add support to use the reserved shared memory within the IoMmu library.
This improves boot times for all SEV guests, with SEV-SNP benefiting the
most as it avoids the page state change call to the hypervisor.
Cc: Erdem Aktas <erdemaktas@google.com> Cc: James Bottomley <jejb@linux.ibm.com> Cc: Jiewen Yao <jiewen.yao@intel.com> Cc: Min Xu <min.m.xu@intel.com> Cc: Gerd Hoffmann <kraxel@redhat.com> Acked-by: Jiewen Yao <Jiewen.yao@intel.com> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>