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_test.go

@@ -0,0 +1,19 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package tpm
+
+import "testing"
+
+func TestPropToString(t *testing.T) {
+	for prop, want := range map[uint32]string{
+		0:          "",
+		0x4D534654: "MSFT",
+		0x414D4400: "AMD",
+		0x414D440D: "AMD",
+	} {
+		if got := propToString(prop); got != want {
+			t.Errorf("propToString(0x%x): got %q, want %q", prop, got, want)
+		}
+	}
+}