KVM: x86/mmu: Derive EPT violation RWX bits from EPTE RWX bits

Derive the mask of RWX bits reported on EPT violations from the mask of
RWX bits that are shoved into EPT entries; the layout is the same, the
EPT violation bits are simply shifted by three.  Use the new shift and a
slight copy-paste of the mask derivation instead of completely open
coding the same to convert between the EPT entry bits and the exit
qualification when synthesizing a nested EPT Violation.

No functional change intended.

Cc: SU Hang <darcy.sh@antgroup.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220329030108.97341-3-darcy.sh@antgroup.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>