meta-tpm: add layer sanity check

Signed-off-by: Armin Kuster <akuster808@gmail.com>

meta-tpm/classes/sanity-meta-tpm.bbclass

@@ -0,0 +1,10 @@
+addhandler tpm_machinecheck
+tpm_machinecheck[eventmask] = "bb.event.SanityCheck"
+python tpm_machinecheck() {
+    skip_check = e.data.getVar('SKIP_META_TPM_SANITY_CHECK') == "1"
+    if 'tpm' not in e.data.getVar('DISTRO_FEATURES').split() and not skip_check:
+        bb.warn("You have included the meta-tpm layer, but \
+'tpm or tpm2' has not been enabled in your DISTRO_FEATURES. Some bbappend files \
+and preferred version setting may not take effect. See the meta-tpm README \
+for details on enabling tpm support.")
+}