OvmfPkg/MemEncryptSevLib: Address range encryption state interface

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3108

Update the MemEncryptSevLib library to include an interface that can
report the encryption state on a range of memory. The values will
represent the range as being unencrypted, encrypted, a mix of unencrypted
and encrypted, and error (e.g. ranges that aren't mapped).

Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <0d98f4d42a2b67310c29bac7bcdcf1eda6835847.1610045305.git.thomas.lendacky@amd.com>

OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecVirtualMemory.c

@@ -13,6 +13,26 @@
 
 #include "VirtualMemory.h"
 
+/**
+  Return the pagetable memory encryption mask.
+
+  @return  The pagetable memory encryption mask.
+
+**/
+UINT64
+EFIAPI
+InternalGetMemEncryptionAddressMask (
+  VOID
+  )
+{
+  UINT64                            EncryptionMask;
+
+  EncryptionMask = MemEncryptSevGetEncryptionMask ();
+  EncryptionMask &= PAGING_1G_ADDRESS_MASK_64;
+
+  return EncryptionMask;
+}
+
 /**
   This function clears memory encryption bit for the memory region specified by
   PhysicalAddress and Length from the current page table context.