hostinfo,tailcfg: report TPM availability on windows/linux (#15831)

Start collecting fleet data on TPM availability via hostinfo.

Updates #15830

Signed-off-by: Andrew Lytvynov <awly@tailscale.com>

feature/tpm/tpm_linux.go

@@ -0,0 +1,18 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package tpm
+
+import (
+	"github.com/google/go-tpm/tpm2/transport/linuxtpm"
+	"tailscale.com/tailcfg"
+)
+
+func info() *tailcfg.TPMInfo {
+	t, err := linuxtpm.Open("/dev/tpm0")
+	if err != nil {
+		return nil
+	}
+	defer t.Close()
+	return infoFromCapabilities(t)
+}