KVM: x86: Add macro to ensure reserved cr4 bits checks stay in sync

Add a helper macro to generate the set of reserved cr4 bits for both
host and guest to ensure that adding a check on guest capabilities is
also added for host capabilities, and vice versa.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>