MdeModulePkg/FaultTolerantWriteDxe: factor out boot service accesses

In preparation of providing a standalone MM based FTW driver, move
the existing SMM driver to the new MM services table, and factor out
some pieces that are specific to the traditional driver, mainly
related to the use of UEFI boot services, which are not accessible
to standalone MM drivers.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jian J Wang <jian.j.wang@intel.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>

MdeModulePkg/Universal/FaultTolerantWriteDxe/FaultTolerantWriteDxe.c

@@ -51,6 +51,7 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 
 **/
 
+#include <Library/UefiBootServicesTableLib.h>
 #include "FaultTolerantWrite.h"
 EFI_EVENT                                 mFvbRegistration = NULL;
 
@@ -250,3 +251,33 @@ FaultTolerantWriteInitialize (
 
   return EFI_SUCCESS;
 }
+
+/**
+  Internal implementation of CRC32. Depending on the execution context
+  (traditional SMM or DXE vs standalone MM), this function is implemented
+  via a call to the CalculateCrc32 () boot service, or via a library
+  call.
+
+  If Buffer is NULL, then ASSERT().
+  If Length is greater than (MAX_ADDRESS - Buffer + 1), then ASSERT().
+
+  @param[in]  Buffer       A pointer to the buffer on which the 32-bit CRC is to be computed.
+  @param[in]  Length       The number of bytes in the buffer Data.
+
+  @retval Crc32            The 32-bit CRC was computed for the data buffer.
+
+**/
+UINT32
+FtwCalculateCrc32 (
+  IN  VOID                         *Buffer,
+  IN  UINTN                        Length
+  )
+{
+  EFI_STATUS    Status;
+  UINT32        ReturnValue;
+
+  Status = gBS->CalculateCrc32 (Buffer, Length, &ReturnValue);
+  ASSERT_EFI_ERROR (Status);
+
+  return ReturnValue;
+}