OvmfPkg: Update IoMmuDxe to support TDX

OvmfPkg: Update IoMmuDxe to support TDX

RFC: https://bugzilla.tianocore.org/show_bug.cgi?id=3429

The IOMMU protocol driver provides capabilities to set a DMA access
attribute and methods to allocate, free, map and unmap the DMA memory
for the PCI Bus devices.

The current IoMmuDxe driver supports DMA operations inside SEV guest.
To support DMA operation in TDX guest,
CC_GUEST_IS_XXX (PcdConfidentialComputingGuestAttr) is used to determine
if it is SEV guest or TDX guest.

Due to security reasons all DMA operations inside the SEV/TDX guest must
be performed on shared pages. The IOMMU protocol driver for the SEV/TDX
guest uses a bounce buffer to map guest DMA buffer to shared pages in
order to provide the support for DMA operations inside SEV/TDX guest.

The call of SEV or TDX specific function to set/clear EncMask/SharedBit
is determined by CC_GUEST_IS_XXX (PcdConfidentialComputingGuestAttr).

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: James Bottomley <jejb@linux.ibm.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Signed-off-by: Min Xu <min.m.xu@intel.com>