KVM: x86/mmu: Fix use of enums in trace_fast_page_fault

Enum values have to be exported to userspace since the formatting is not
done in the kernel. Without doing this perf maps RET_PF_FIXED and
RET_PF_SPURIOUS to 0, which results in incorrect output:

  $ perf record -a -e kvmmmu:fast_page_fault --filter "ret==3" -- ./access_tracking_perf_test
  $ perf script | head -1
   [...] new 610006048d25877 spurious 0 fixed 0  <------ should be 1

Fix this by exporting the enum values to userspace with TRACE_DEFINE_ENUM.

Fixes: c4371c2a ("KVM: x86/mmu: Return unique RET_PF_* values if the fault was fixed")
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20210713220957.3493520-3-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>