KVM: x86/mmu: Use is_removed_spte() instead of open coded equivalents

mainline inclusion
from mainline-v5.13-rc1
commit 7a51393a
category: feature
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I7S3VQ
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7a51393ae0f6287f9b2bdd138f5a091b7c302c1f



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Use the is_removed_spte() helper instead of open coding the check.

No functional change intended.

Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210225204749.1512652-23-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>