KVM: Documentation: Add disable pause exits to KVM_CAP_X86_DISABLE_EXITS

Commit b31c114b (KVM: X86: Provide a capability to disable PAUSE intercepts)
forgot to add the KVM_X86_DISABLE_EXITS_PAUSE into api doc. This patch adds
it.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Documentation/virtual/kvm/api.txt

@@ -4893,6 +4893,7 @@ Valid bits in args[0] are
 
 #define KVM_X86_DISABLE_EXITS_MWAIT            (1 << 0)
 #define KVM_X86_DISABLE_EXITS_HLT              (1 << 1)
+#define KVM_X86_DISABLE_EXITS_PAUSE            (1 << 2)
 
 Enabling this capability on a VM provides userspace with a way to no
 longer intercept some instructions for improved latency in some