Add freeform to the allow list to carry a PE32 image (#1938)

## Description

This change is added to allow carrying the rust supervisor as a PE32
section in the FV as freeform file type.

For details on how to complete these options and their meaning refer to
[CONTRIBUTING.md](https://github.com/microsoft/mu/blob/HEAD/CONTRIBUTING.md).

- [ ] Impacts functionality?
- [ ] Impacts security?
- [ ] Breaking change?
- [ ] Includes tests?
- [ ] Includes documentation?

## How This Was Tested

The `FREEFORM` FFS entry can now carry a PE32 section without failing
the validation

## Integration Instructions

N/A

Author: kuqin12

.pytool/Plugin/ImageValidation/image_validation.cfg

@@ -29,6 +29,7 @@ IMAGE_FILE_MACHINE_AMD64:
     UEFI_APPLICATION: {}
     UEFI_DRIVER: {}
     USER_DEFINED: {}
+    FREEFORM: {}
 
 IMAGE_FILE_MACHINE_ARM64:
     DEFAULT:
@@ -55,6 +56,7 @@ IMAGE_FILE_MACHINE_ARM64:
     UEFI_APPLICATION: {}
     UEFI_DRIVER: {}
     USER_DEFINED: {}
+    FREEFORM: {}
 
 IMAGE_FILE_MACHINE_I386:
     DEFAULT:
@@ -63,8 +65,10 @@ IMAGE_FILE_MACHINE_I386:
     PEI_CORE: {}
     SEC: {}
     USER_DEFINED: {}
+    FREEFORM: {}
 
 IMAGE_FILE_MACHINE_ARM:
     DEFAULT:
         DATA_CODE_SEPARATION: false
     USER_DEFINED: {}
+    FREEFORM: {}