KVM: VMX: Use vpid_sync_context() directly when possible

Use vpid_sync_context() directly for flows that run if and only if
enable_vpid=1, or more specifically, nested VMX flows that are gated by
vmx->nested.msrs.secondary_ctls_high.SECONDARY_EXEC_ENABLE_VPID being
set, which is allowed if and only if enable_vpid=1.  Because these flows
call __vmx_flush_tlb() with @invalidate_gpa=false, the if-statement that
decides between INVEPT and INVVPID will always go down the INVVPID path,
i.e. call vpid_sync_context() because
"enable_ept && (invalidate_gpa || !enable_vpid)" always evaluates false.

This helps pave the way toward removing @invalidate_gpa and @vpid from
__vmx_flush_tlb() and its callers.

Opportunstically drop unnecessary brackets in handle_invvpid() around an
affected __vmx_flush_tlb()->vpid_sync_context() conversion.

No functional change intended.

Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200320212833.3507-10-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>