KVM: selftests: guest_memfd mmap() test when mmap is supported

KVM: selftests: guest_memfd mmap() test when mmap is supported

Expand the guest_memfd selftests to comprehensively test host userspace
mmap functionality for guest_memfd-backed memory when supported by the
VM type.

Introduce new test cases to verify the following:

* Successful mmap operations: Ensure that MAP_SHARED mappings succeed
  when guest_memfd mmap is enabled.

* Data integrity: Validate that data written to the mmap'd region is
  correctly persistent and readable.

* fallocate interaction: Test that fallocate(FALLOC_FL_PUNCH_HOLE)
  correctly zeros out mapped pages.

* Out-of-bounds access: Verify that accessing memory beyond the
  guest_memfd's size correctly triggers a SIGBUS signal.

* Unsupported mmap: Confirm that mmap attempts fail as expected when
  guest_memfd mmap support is not enabled for the specific guest_memfd
  instance or VM type.

* Flag validity: Introduce test_vm_type_gmem_flag_validity() to
  systematically test that only allowed guest_memfd creation flags are
  accepted for different VM types (e.g., GUEST_MEMFD_FLAG_MMAP for
  default VMs, no flags for CoCo VMs).

The existing tests for guest_memfd creation (multiple instances, invalid
sizes), file read/write, file size, and invalid punch hole operations
are integrated into the new test_with_type() framework to allow testing
across different VM types.

Cc: James Houghton <jthoughton@google.com>
Cc: Gavin Shan <gshan@redhat.com>
Cc: Shivank Garg <shivankg@amd.com>
Co-developed-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Signed-off-by: Fuad Tabba <tabba@google.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20250729225455.670324-24-seanjc@google.com>
[Fix default vm_types to use BIT() - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>