BaseTools: Support COMPAT16 section generation

Currently COMPAT16 section type is not recognized and GenSec is called
without the "-s [SectionType]" argument.
Add COMPAT16 type to the SectionType dictionary to fix the issue.

Now this syntax works correctly:
```
FILE FREEFORM = <GUID>  {
  SECTION COMPAT16 = <FILE>
}
```

Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>

BaseTools/Source/Python/GenFds/Section.py

@@ -28,6 +28,7 @@ class Section (SectionClassObject):
         BINARY_FILE_TYPE_PIC       : 'EFI_SECTION_PIC',
         BINARY_FILE_TYPE_TE        : 'EFI_SECTION_TE',
         'FV_IMAGE'  : 'EFI_SECTION_FIRMWARE_VOLUME_IMAGE',
+        'COMPAT16'  : 'EFI_SECTION_COMPATIBILITY16',
         BINARY_FILE_TYPE_DXE_DEPEX : 'EFI_SECTION_DXE_DEPEX',
         BINARY_FILE_TYPE_PEI_DEPEX : 'EFI_SECTION_PEI_DEPEX',
         'GUIDED'    : 'EFI_SECTION_GUID_DEFINED',